DOC: update the Series.sort_values docstring
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>`
- [ ] The PEP8 style check passes: `git diff upstream/master -u -- "*.py" | flake8 --diff`
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- [ ] It has been proofread on language by another sprint participant

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```
# paste output of "scripts/validate_docstrings.py <your-function-or-method>" here
# between the "```" (remove this comment, but keep the "```")

```

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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

Hello @rafarui! Thanks for submitting the PR.

 - In the file [`pandas/core/series.py`](https://github.com/pandas-dev/pandas/blob/04c8faadee25d631ffd75302ac022d73ff2d66a3/pandas/core/series.py), following are the PEP8 issues :

> [Line 1888:5](https://github.com/pandas-dev/pandas/blob/04c8faadee25d631ffd75302ac022d73ff2d66a3/pandas/core/series.py#L1888): [E265](https://duckduckgo.com/?q=pep8%20E265) block comment should start with '# '
> [Line 1894:80](https://github.com/pandas-dev/pandas/blob/04c8faadee25d631ffd75302ac022d73ff2d66a3/pandas/core/series.py#L1894): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (86 > 79 characters)
> [Line 1905:80](https://github.com/pandas-dev/pandas/blob/04c8faadee25d631ffd75302ac022d73ff2d66a3/pandas/core/series.py#L1905): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (123 > 79 characters)
> [Line 1908:80](https://github.com/pandas-dev/pandas/blob/04c8faadee25d631ffd75302ac022d73ff2d66a3/pandas/core/series.py#L1908): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (86 > 79 characters)
> [Line 1923:80](https://github.com/pandas-dev/pandas/blob/04c8faadee25d631ffd75302ac022d73ff2d66a3/pandas/core/series.py#L1923): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (83 > 79 characters)

 @rafarui do you wish to continue working on this?  Sorry we didn't have a chance to review it yesterdya, but if you reopen I'll take a look. @TomAugspurger 
No need, I had opened this pull request by mistake. The "right"one is this one
https://github.com/pandas-dev/pandas/pull/20247

Thanks