DOC: update pandas.Series.rename_axis

[xrmx]

Checklist for the pandas documentation sprint (ignore this if you are doing
an unrelated PR):

• PR title is "DOC: update the docstring"
• 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
• The html version looks good: python doc/make.py --single <your-function-or-method>
• It has been proofread on language by another sprint participant

Please include the output of the validation script below between the "```" ticks:

################################################################################
############# Docstring (pandas.core.generic.NDFrame.rename_axis)  #############
################################################################################

Alter the name of the index or columns.

This function alters the name of the index or columns.

Parameters
----------
mapper : scalar, list-like, optional
    Value to set the axis name attribute.
axis : int, str, default 0
    The index or the name of the axis.
copy : boolean, default True
    Also copy underlying data.
inplace : boolean, default False
    Modifies the mapper in place.

Returns
-------
type of caller or None if inplace=True
    Renamed

Notes
-----
Prior to version 0.21.0, ``rename_axis`` could also be used to change
the axis *labels* by passing a mapping or scalar. This behavior is
deprecated and will be removed in a future version. Use ``rename``
instead.

See Also
--------
pandas.Series.rename : Alter Series index labels or name
pandas.DataFrame.rename : Alter DataFrame index labels or name
pandas.Index.rename : Set new names on index

Examples
--------
>>> df = pd.DataFrame({"A": [1, 2, 3], "B": [4, 5, 6]})
>>> df.rename_axis("foo")
     A  B
foo
0    1  4
1    2  5
2    3  6

>>> df.rename_axis("bar", axis="columns")
bar  A  B
0    1  4
1    2  5
2    3  6

################################################################################
################################## Validation ##################################
################################################################################

Docstring for "pandas.core.generic.NDFrame.rename_axis" correct. :)

[TomAugspurger]

Since this is just restating the short summary I think it can be removed.

[xrmx]

Done.

[TomAugspurger]

Where inconsistent with axis. But

        axis : {0 or 'index', 1 or 'columns'}, default 0

seems to be the most common.

[xrmx]

Done

[TomAugspurger]

I think this should be

renamed : Series, DataFrame, or None
    The same type as the caller or None if `inplace` is True.

[xrmx]

Done

[xrmx]

Updated PR after review, thanks!

[codecov]

Codecov Report

Merging #20137 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #20137      +/-   ##
==========================================
- Coverage   91.72%   91.72%   -0.01%     
==========================================
  Files         150      150              
  Lines       49156    49152       -4     
==========================================
- Hits        45090    45086       -4     
  Misses       4066     4066

Flag	Coverage Δ
#multiple	90.11% <ø> (-0.01%)	⬇️
#single	41.84% <ø> (-0.01%)	⬇️

Impacted Files	Coverage Δ
pandas/core/generic.py	95.84% <ø> (ø)	⬆️
pandas/core/base.py	96.78% <0%> (-0.02%)	⬇️
pandas/core/series.py	93.85% <0%> (-0.01%)	⬇️
pandas/core/indexes/base.py	96.66% <0%> (-0.01%)	⬇️
pandas/core/indexes/multi.py	95.06% <0%> (ø)	⬆️

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[TomAugspurger]

Added a series example. Thanks @xrmx!