DOC: update the pandas.Series.dt.total_seconds docstring
State: closed

Checklist for the pandas documentation sprint (ignore this if you are doing
an unrelated PR):

- [X] PR title is "DOC: update the <your-function-or-method> docstring"
- [X] The validation script passes: `scripts/validate_docstrings.py <your-function-or-method>`
- [X] The PEP8 style check passes: `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [X] The html version looks good: `python doc/make.py --single <your-function-or-method>`
- [X] It has been proofread on language by another sprint participant

Please include the output of the validation script below between the "```" ticks:

```
################################################################################
################## Docstring (pandas.Series.dt.total_seconds) ##################
################################################################################

Return total duration of each element expressed in seconds.

Return a series with the same length and index as the original,
containing the length of each element expressed in seconds.

Returns
-------
s : pandas.Series
    a series of type `float64`.

Examples
--------
>>> s = pd.Series(pd.to_timedelta(np.arange(5), unit='d'))
>>> s
0   0 days
1   1 days
2   2 days
3   3 days
4   4 days
dtype: timedelta64[ns]
>>> s.dt.total_seconds()
0         0.0
1     86400.0
2    172800.0
3    259200.0
4    345600.0
dtype: float64

################################################################################
################################## Validation ##################################
################################################################################

Errors found:
        Errors in parameters section
                Parameters {'args', 'kwargs'} not documented
        See Also section not found

```

If the validation script still gives errors, but you think there is a good reason
to deviate in this case (and there are certainly such cases), please state this
explicitly.


Checklist for other PRs (remove this part if you are doing a PR for the pandas documentation sprint):

- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry


Labels:
name: Docs
name: Datetime
description: Datetime data dtype
name: Timedelta
description: Timedelta data type

Comments:
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> The diff coverage is `n/a`.

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@@            Coverage Diff             @@
##           master   #20159      +/-   ##
==========================================
- Coverage   91.72%    91.7%   -0.03%     
==========================================
  Files         150      150              
  Lines       49156    49165       +9     
==========================================
- Hits        45090    45087       -3     
- Misses       4066     4078      +12
```

| Flag | Coverage Δ | |
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| [pandas/core/indexes/timedeltas.py](https://codecov.io/gh/pandas-dev/pandas/pull/20159/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy90aW1lZGVsdGFzLnB5) | `91.03% <ø> (ø)` | :arrow_up: |
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| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/20159/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `93.84% <0%> (-0.02%)` | :arrow_down: |
| [pandas/core/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/20159/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYmFzZS5weQ==) | `96.78% <0%> (-0.02%)` | :arrow_down: |
| [pandas/core/indexes/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/20159/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9iYXNlLnB5) | `96.66% <0%> (-0.01%)` | :arrow_down: |
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| [pandas/core/indexing.py](https://codecov.io/gh/pandas-dev/pandas/pull/20159/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhpbmcucHk=) | `93.02% <0%> (ø)` | :arrow_up: |
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| [pandas/plotting/\_misc.py](https://codecov.io/gh/pandas-dev/pandas/pull/20159/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19taXNjLnB5) | `38.98% <0%> (ø)` | :arrow_up: |
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| ... and [8 more](https://codecov.io/gh/pandas-dev/pandas/pull/20159/diff?src=pr&el=tree-more) | |

------

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Made this generic for TimedeltaIndex and Series[timedelta64].
Yes, that looks like a good solution