DOC: Updated kurt docstring (for pandas sprint)
Assigned docstring for pandas documentation sprint

Please note that I also removed **kwargs from the call signature here as they were not being used, so I thought it would be strange to document. For what it's worth I started a discussion on the G[oogle groups list ](https://groups.google.com/forum/#!topic/pandas-documentation-sprint/P5_av_VuV6E)to see if that's the best way to handle or if we wanted to go a different path
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19999?src=pr&el=h1) Report
> Merging [#19999](https://codecov.io/gh/pandas-dev/pandas/pull/19999?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/e02f73787bfbd00ce2ad899542538dfad854eb01?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19999/graphs/tree.svg?token=eZ4WkYLtcO&width=650&src=pr&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/19999?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #19999      +/-   ##
==========================================
+ Coverage   91.67%   91.67%   +<.01%     
==========================================
  Files         150      150              
  Lines       49096    49094       -2     
==========================================
  Hits        45007    45007              
+ Misses       4089     4087       -2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.05% <100%> (ø)` | :arrow_up: |
| #single | `41.87% <100%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/19999?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/window.py](https://codecov.io/gh/pandas-dev/pandas/pull/19999/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvd2luZG93LnB5) | `96.31% <100%> (-0.01%)` | :arrow_down: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/19999/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `83.85% <0%> (+0.2%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19999?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19999?src=pr&el=footer). Last update [e02f737...dd61858](https://codecov.io/gh/pandas-dev/pandas/pull/19999?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 So based on both of your feedback I'm wondering if we should update the `_doc_template` in this module to look as follows:

```python
_doc_template = """

Returns
-------
Series or DataFrame (matches input)
    Like-indexed object containing the result of function application

See also
--------
pandas.Series.%(name)s
pandas.DataFrame.%(name)s
%(other_see_alsos)
"""
```

This would ensure that we consistently always have `pandas.Series.rolling` and `pandas.DataFrame.rolling` as part of every function, but also give it the flexibility to add more references. 

The downside here is at the moment I don't think that there's a way to add `%(other_see_alsos)` without explicitly wrapping all of the other methods in the module with a substitution that provides it. Alternately we could update the `Substitution` class to allow for optional keyword specification, but I'd worry about a lack of explicitness there.

Anyway wanted to get your feedback before going further - do you think the above template is a good idea and if so if it's worth me going and updating all of the `@Substitution` decorators in this module to contain `other_see_also=""` prior to the sprint? @WillAyd I'm fine with both options (only updating this docstring here, or updating the template as well). 

The question is a bit how well the template will scale if all docstrings have a custom extended summary, examples, notes etc, only to share the 'returns' and 'see also' section thanks! @jreback please wait a bit with merging the 'test' PRs for the sprint for now. Let's leave time to comment on them.  np

just wanted to clear backlog

i wont merge doc prs then u less u approve > i wont merge doc prs then u less u approve

It's also that for the test PRs now want to keep them open a bit so other organizers can look and review. @WillAyd feel free to open a new PR for my remaining comments