Update README.md

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<details>
<summary>Show benchmarks</summary>

PyArrow==8.0.0

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.008370 / 0.011353 (-0.002983) | 0.004674 / 0.011008 (-0.006334) | 0.103912 / 0.038508 (0.065404) | 0.101668 / 0.023109 (0.078559) | 0.417945 / 0.275898 (0.142047) | 0.454805 / 0.323480 (0.131325) | 0.004763 / 0.007986 (-0.003223) | 0.003934 / 0.004328 (-0.000394) | 0.078446 / 0.004250 (0.074196) | 0.068383 / 0.037052 (0.031331) | 0.415100 / 0.258489 (0.156611) | 0.475272 / 0.293841 (0.181431) | 0.036884 / 0.128546 (-0.091662) | 0.010097 / 0.075646 (-0.065549) | 0.354962 / 0.419271 (-0.064309) | 0.062688 / 0.043533 (0.019155) | 0.420643 / 0.255139 (0.165504) | 0.446504 / 0.283200 (0.163304) | 0.029075 / 0.141683 (-0.112608) | 1.791517 / 1.452155 (0.339363) | 1.859820 / 1.492716 (0.367104) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.246929 / 0.018006 (0.228923) | 0.519593 / 0.000490 (0.519103) | 0.006848 / 0.000200 (0.006648) | 0.000168 / 0.000054 (0.000114) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.035179 / 0.037411 (-0.002232) | 0.115582 / 0.014526 (0.101057) | 0.128235 / 0.176557 (-0.048321) | 0.187123 / 0.737135 (-0.550012) | 0.120862 / 0.296338 (-0.175477) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.463406 / 0.215209 (0.248197) | 4.615517 / 2.077655 (2.537863) | 2.250513 / 1.504120 (0.746393) | 2.061226 / 1.541195 (0.520032) | 2.189938 / 1.468490 (0.721448) | 0.582984 / 4.584777 (-4.001793) | 4.299464 / 3.745712 (0.553751) | 4.037274 / 5.269862 (-1.232588) | 2.608967 / 4.565676 (-1.956710) | 0.068944 / 0.424275 (-0.355331) | 0.009501 / 0.007607 (0.001894) | 0.567436 / 0.226044 (0.341392) | 5.662738 / 2.268929 (3.393809) | 2.849094 / 55.444624 (-52.595530) | 2.461013 / 6.876477 (-4.415464) | 2.663245 / 2.142072 (0.521172) | 0.704528 / 4.805227 (-4.100699) | 0.163583 / 6.500664 (-6.337081) | 0.075719 / 0.075469 (0.000250) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.604743 / 1.841788 (-0.237044) | 24.512054 / 8.074308 (16.437746) | 17.870939 / 10.191392 (7.679547) | 0.199188 / 0.680424 (-0.481236) | 0.023820 / 0.534201 (-0.510381) | 0.487520 / 0.579283 (-0.091763) | 0.512543 / 0.434364 (0.078179) | 0.575138 / 0.540337 (0.034801) | 0.759863 / 1.386936 (-0.627073) |

</details>
PyArrow==latest

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.010516 / 0.011353 (-0.000837) | 0.004779 / 0.011008 (-0.006229) | 0.078482 / 0.038508 (0.039974) | 0.108533 / 0.023109 (0.085424) | 0.498692 / 0.275898 (0.222794) | 0.534698 / 0.323480 (0.211218) | 0.007624 / 0.007986 (-0.000362) | 0.003938 / 0.004328 (-0.000391) | 0.077317 / 0.004250 (0.073067) | 0.078056 / 0.037052 (0.041004) | 0.493648 / 0.258489 (0.235159) | 0.540891 / 0.293841 (0.247050) | 0.040377 / 0.128546 (-0.088169) | 0.010155 / 0.075646 (-0.065491) | 0.084384 / 0.419271 (-0.334888) | 0.061419 / 0.043533 (0.017886) | 0.494474 / 0.255139 (0.239335) | 0.524656 / 0.283200 (0.241456) | 0.029052 / 0.141683 (-0.112631) | 1.794584 / 1.452155 (0.342429) | 1.939987 / 1.492716 (0.447270) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.377404 / 0.018006 (0.359398) | 0.516562 / 0.000490 (0.516072) | 0.109555 / 0.000200 (0.109356) | 0.001126 / 0.000054 (0.001071) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.039793 / 0.037411 (0.002382) | 0.123001 / 0.014526 (0.108475) | 0.127536 / 0.176557 (-0.049021) | 0.191681 / 0.737135 (-0.545455) | 0.128590 / 0.296338 (-0.167748) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.513689 / 0.215209 (0.298480) | 5.135114 / 2.077655 (3.057459) | 2.797885 / 1.504120 (1.293765) | 2.715332 / 1.541195 (1.174137) | 2.746437 / 1.468490 (1.277947) | 0.596480 / 4.584777 (-3.988297) | 4.382013 / 3.745712 (0.636301) | 3.965956 / 5.269862 (-1.303906) | 2.545206 / 4.565676 (-2.020471) | 0.069620 / 0.424275 (-0.354655) | 0.009321 / 0.007607 (0.001714) | 0.612424 / 0.226044 (0.386379) | 6.107037 / 2.268929 (3.838109) | 3.447246 / 55.444624 (-51.997379) | 3.073262 / 6.876477 (-3.803215) | 3.280185 / 2.142072 (1.138113) | 0.704776 / 4.805227 (-4.100451) | 0.160488 / 6.500664 (-6.340176) | 0.075730 / 0.075469 (0.000261) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.697035 / 1.841788 (-0.144753) | 24.766118 / 8.074308 (16.691809) | 18.476699 / 10.191392 (8.285307) | 0.176594 / 0.680424 (-0.503830) | 0.024249 / 0.534201 (-0.509952) | 0.478743 / 0.579283 (-0.100541) | 0.518774 / 0.434364 (0.084410) | 0.581498 / 0.540337 (0.041161) | 0.797784 / 1.386936 (-0.589152) |

</details>
</details>

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