DOC: Update the pandas.Series.str.count() 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"
- [ ] 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.count)  #####################
################################################################################

Count occurrences of pattern in each string of the Series/Index.

This function is used to count the number of times a particular regex
pattern is repeated in each of the string elements of the
:class:`~pandas.Series`.

Parameters
----------
pat : str
    Valid regular expression.
flags : int, default 0, meaning no flags
    Flags for re module, e.g. re.IGNORECASE.

Returns
-------
counts : Series/Index of integer values

Notes
-----
Some characters need to be escaped when passing in pat.
eg. '$' has a special meaning in regex and must be escaped when finding
specifically this char.

Examples
--------
Take a look at
`this link <https://docs.python.org/3/howto/regex.html#compilation-flags>`_
for the list of all possible flags that can be used.

>>> s = pd.Series(['A', 'B', 'Aaba', 'Baca', np.nan, 'CABA', 'cat'])
>>> s.str.count('a')
0    0.0
1    0.0
2    2.0
3    2.0
4    NaN
5    0.0
6    1.0
dtype: float64

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

Errors found:
	Errors in parameters section
		Parameters {'kwargs'} not documented
	See Also section not found

```
As discussed in the gitter channel it was suggested to ignore kwargs for now.
Not sure what should be a part of see also here.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20154?src=pr&el=h1) Report
> Merging [#20154](https://codecov.io/gh/pandas-dev/pandas/pull/20154?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/840d4323935348a890d6b868f2b18e8dddd22199?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/20154/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/20154?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #20154      +/-   ##
==========================================
- 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%)` | :arrow_down: |
| #single | `41.84% <ø> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/20154?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/strings.py](https://codecov.io/gh/pandas-dev/pandas/pull/20154/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3RyaW5ncy5weQ==) | `98.32% <ø> (ø)` | :arrow_up: |
| [pandas/core/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/20154/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYmFzZS5weQ==) | `96.78% <0%> (-0.02%)` | :arrow_down: |
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/20154/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `93.85% <0%> (-0.01%)` | :arrow_down: |
| [pandas/core/indexes/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/20154/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9iYXNlLnB5) | `96.66% <0%> (-0.01%)` | :arrow_down: |
| [pandas/core/indexes/multi.py](https://codecov.io/gh/pandas-dev/pandas/pull/20154/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9tdWx0aS5weQ==) | `95.06% <0%> (ø)` | :arrow_up: |
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/20154/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `95.84% <0%> (ø)` | :arrow_up: |
| [pandas/plotting/\_core.py](https://codecov.io/gh/pandas-dev/pandas/pull/20154/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb3JlLnB5) | `82.23% <0%> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20154?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/20154?src=pr&el=footer). Last update [840d432...93d2257](https://codecov.io/gh/pandas-dev/pandas/pull/20154?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @TomAugspurger please take a look at the update Thanks!