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


@darke-spirits do you have time do update the PR based on the feedback? # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20199?src=pr&el=h1) Report
> Merging [#20199](https://codecov.io/gh/pandas-dev/pandas/pull/20199?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/6008d75ac00aa7c3052b74bf4f6eb73beeaf56a6?src=pr&el=desc) will **decrease** coverage by `0.17%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/20199/graphs/tree.svg?height=150&width=650&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/20199?src=pr&el=tree)

```diff
@@            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%)` | :arrow_down: |
| #single | `41.84% <ø> (-0.26%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/20199?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/strings.py](https://codecov.io/gh/pandas-dev/pandas/pull/20199/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3RyaW5ncy5weQ==) | `98.32% <ø> (-0.31%)` | :arrow_down: |
| [pandas/plotting/\_compat.py](https://codecov.io/gh/pandas-dev/pandas/pull/20199/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb21wYXQucHk=) | `62% <0%> (-28.91%)` | :arrow_down: |
| [pandas/io/s3.py](https://codecov.io/gh/pandas-dev/pandas/pull/20199/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3MzLnB5) | `72.72% <0%> (-13.64%)` | :arrow_down: |
| [pandas/core/arrays/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/20199/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2Jhc2UucHk=) | `74.35% <0%> (-13.5%)` | :arrow_down: |
| [pandas/io/formats/terminal.py](https://codecov.io/gh/pandas-dev/pandas/pull/20199/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvdGVybWluYWwucHk=) | `16.43% <0%> (-4.55%)` | :arrow_down: |
| [pandas/io/formats/printing.py](https://codecov.io/gh/pandas-dev/pandas/pull/20199/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvcHJpbnRpbmcucHk=) | `89.38% <0%> (-3.71%)` | :arrow_down: |
| [pandas/io/html.py](https://codecov.io/gh/pandas-dev/pandas/pull/20199/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2h0bWwucHk=) | `86.6% <0%> (-2.57%)` | :arrow_down: |
| [pandas/io/formats/format.py](https://codecov.io/gh/pandas-dev/pandas/pull/20199/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvZm9ybWF0LnB5) | `96.26% <0%> (-1.99%)` | :arrow_down: |
| [pandas/io/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/20199/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2NvbW1vbi5weQ==) | `68.77% <0%> (-1.88%)` | :arrow_down: |
| [pandas/core/indexes/period.py](https://codecov.io/gh/pandas-dev/pandas/pull/20199/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9wZXJpb2QucHk=) | `92.61% <0%> (-1.8%)` | :arrow_down: |
| ... and [81 more](https://codecov.io/gh/pandas-dev/pandas/pull/20199/diff?src=pr&el=tree-more) | |

------

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> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20199?src=pr&el=footer). Last update [6008d75...8d5ef6e](https://codecov.io/gh/pandas-dev/pandas/pull/20199?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Thanks @darke-spirits for the contribution!