DOC: update the pandas.Series.str.rpartition() docstring (Delhi)

[schopra6]

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.Series.str.rpartition) ###################
################################################################################

Split the string at the last occurrence of `sep`.

This method splits the string at the last occurrence of `sep`,
and return 3 elements containing the part before the separator,
the separator itself, and the part after the separator.
If the separator is not found, return 3 elements containing two empty strings, followed by the string itself.

Parameters
----------
pat : string, default whitespace
    String to split on.
expand : bool, default True
    If True, return DataFrame/MultiIndex expanding dimensionality.
    If False, return Series/Index.

Returns
-------
split : DataFrame/MultiIndex or Series/Index of objects

See Also
--------
partition : Split the string at the first occurrence of `sep`

Examples
--------

>>> s = pd.Series(['A_B_C', 'D_E_F', 'X'])
>>> s
0    A_B_C
1    D_E_F
2        X
dtype: object

>>> s.str.partition('_')
   0  1    2
0  A  _  B_C
1  D  _  E_F
2  X

>>> s.str.rpartition('_')
     0  1  2
0  A_B  _  C
1  D_E  _  F
2          X

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

Docstring for "pandas.Series.str.rpartition" correct. :)

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.

[TomAugspurger]

"return" -> "returns"

[TomAugspurger]

This docstring is shared with the Index. Could you add a short example with Index as well? (can be the same data as this one, just in Index instead of Series.

[jorisvandenbossche]

@darke-spirits do you have time do update the PR based on the feedback?

[codecov]

Codecov Report

Merging #20199 into master will decrease coverage by 0.17%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #20199      +/-   ##
==========================================
- Coverage    91.9%   91.72%   -0.18%     
==========================================
  Files         160      150      -10     
  Lines       49904    49152     -752     
==========================================
- Hits        45864    45086     -778     
- Misses       4040     4066      +26

Flag	Coverage Δ
#multiple	90.11% <ø> (-0.18%)	⬇️
#single	41.84% <ø> (-0.26%)	⬇️

Impacted Files	Coverage Δ
pandas/core/strings.py	98.32% <ø> (-0.31%)	⬇️
pandas/plotting/_compat.py	62% <0%> (-28.91%)	⬇️
pandas/io/s3.py	72.72% <0%> (-13.64%)	⬇️
pandas/core/arrays/base.py	74.35% <0%> (-13.5%)	⬇️
pandas/io/formats/terminal.py	16.43% <0%> (-4.55%)	⬇️
pandas/io/formats/printing.py	89.38% <0%> (-3.71%)	⬇️
pandas/io/html.py	86.6% <0%> (-2.57%)	⬇️
pandas/io/formats/format.py	96.26% <0%> (-1.99%)	⬇️
pandas/io/common.py	68.77% <0%> (-1.88%)	⬇️
pandas/core/indexes/period.py	92.61% <0%> (-1.8%)	⬇️
... and 81 more

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[datapythonista]

Thanks @darke-spirits for the contribution!