[Benchmark] Readme for benchmark
Author: patrickvonplaten
Pull request: yes

At @sshleifer, @julien-c, @clmnt  - shifting discussion about README.me here to include prev PR: #5360
in v3.0.0

Comments:
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/5363?src=pr&el=h1) Report
> Merging [#5363](https://codecov.io/gh/huggingface/transformers/pull/5363?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/4bcc35cd693cc0f62d2b4853cd8a5db8608a4abd&el=desc) will **decrease** coverage by `0.87%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/5363/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/5363?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #5363      +/-   ##
==========================================
- Coverage   77.65%   76.77%   -0.88%     
==========================================
  Files         138      138              
  Lines       24314    24314              
==========================================
- Hits        18881    18668     -213     
- Misses       5433     5646     +213     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/5363?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/tokenization\_xlm.py](https://codecov.io/gh/huggingface/transformers/pull/5363/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90b2tlbml6YXRpb25feGxtLnB5) | `16.26% <0.00%> (-66.67%)` | :arrow_down: |
| [src/transformers/tokenization\_transfo\_xl.py](https://codecov.io/gh/huggingface/transformers/pull/5363/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90b2tlbml6YXRpb25fdHJhbnNmb194bC5weQ==) | `33.56% <0.00%> (-8.93%)` | :arrow_down: |
| [src/transformers/tokenization\_utils\_base.py](https://codecov.io/gh/huggingface/transformers/pull/5363/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90b2tlbml6YXRpb25fdXRpbHNfYmFzZS5weQ==) | `92.39% <0.00%> (-1.33%)` | :arrow_down: |
| [src/transformers/modeling\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/5363/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl91dGlscy5weQ==) | `87.24% <0.00%> (-0.15%)` | :arrow_down: |
| [src/transformers/configuration\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/5363/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX3V0aWxzLnB5) | `96.40% <0.00%> (+0.71%)` | :arrow_up: |
| [src/transformers/tokenization\_auto.py](https://codecov.io/gh/huggingface/transformers/pull/5363/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90b2tlbml6YXRpb25fYXV0by5weQ==) | `97.77% <0.00%> (+2.22%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/huggingface/transformers/pull/5363?src=pr&el=continue).
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> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/5363?src=pr&el=footer). Last update [4bcc35c...a73a58e](https://codecov.io/gh/huggingface/transformers/pull/5363?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).


@julien-c - should we go for this solution for now instead of letting users adapt a giant csv file?
We can always later adapt the way we present the data since it's just a README

sounds good