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.