DOC: update the Series.memory_usage() docstring
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>`
- [ ] It has been proofread on language by another sprint participant

Output of the validation script:

```
################################################################################
#################### Docstring (pandas.Series.memory_usage) ####################
################################################################################

Return the memory usage of the Series.

The memory usage can optionally include the contribution of
the index and of elements of `object` dtype.

Parameters
----------
index : bool, default True
    Specifies whether to include the memory usage of the Series index.
deep : bool, default False
    If True, introspect the data deeply by interrogating
    `object` dtypes for system-level memory consumption, and include
    it in the returned value.

Returns
-------
int
    Bytes of memory consumed.

See Also
--------
numpy.ndarray.nbytes : Total bytes consumed by the elements of the
    array.

Examples
--------

>>> s = pd.Series(range(3))
>>> s.memory_usage()
104

Not including the index gives the size of the rest of the data, which
is necessarily smaller:

>>> s.memory_usage(index=False)
24

The memory footprint of `object` values is ignored by default:

>>> class MyClass: pass
>>> s = pd.Series(MyClass())
>>> s
0    <__main__.MyClass object at ...>
dtype: object
>>> s.memory_usage()
88
>>> s.memory_usage(deep=True)
120

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

Errors found:
        Examples do not pass tests

################################################################################
################################### Doctests ###################################
################################################################################

**********************************************************************
Line 43, in pandas.Series.memory_usage
Failed example:
    s
Expected:
    0    <__main__.MyClass object at ...>
    dtype: object
Got:
    0    <__main__.MyClass object at 0x10f8076d8>
    dtype: object
```

Error due to following the recommendation about not giving non-reproducible addresses.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20086?src=pr&el=h1) Report
> Merging [#20086](https://codecov.io/gh/pandas-dev/pandas/pull/20086?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/7c14e4f14aff216be558bf5d4d2d00b4838c2360?src=pr&el=desc) will **decrease** coverage by `0.02%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/20086/graphs/tree.svg?token=eZ4WkYLtcO&width=650&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/20086?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #20086      +/-   ##
==========================================
- Coverage   91.72%    91.7%   -0.03%     
==========================================
  Files         150      150              
  Lines       49122    49122              
==========================================
- Hits        45057    45045      -12     
- Misses       4065     4077      +12
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.08% <ø> (-0.03%)` | :arrow_down: |
| #single | `41.86% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/20086?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/20086/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `93.85% <ø> (ø)` | :arrow_up: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/20086/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.07% <0%> (-1.74%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20086?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/20086?src=pr&el=footer). Last update [7c14e4f...cea218f](https://codecov.io/gh/pandas-dev/pandas/pull/20086?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Thanks a lot!