DOC: Update Series.repeat 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>`
- [ 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.repeat) #######################
################################################################################

Repeat elements of a Series.

Each element of the Series is repeated 'repeats' times.

Parameters
----------
repeats : int
    The number of repetitions for each element.
*args
    These parameters will be passed to a validation function.
**kwargs
    These parameters will be passed to a validation function.

See also
--------
Series.append : Concatenate two or more Series.
pandas.concat : Concatenate two or more DataFrames.
numpy.repeat : Repeat elements of an array.

Returns
-------
Series
    The repeated version of the Series.

Examples
--------
>>> df = pd.DataFrame({'col1' : ['A','B','C'],'col2' : [ 0 , 1 , 2 ]})
>>> df
col1  col2
0    A     0
1    B     1
2    C     2
>>> df.col1.repeat(3)
0    A
0    A
0    A
1    B
1    B
1    B
2    C
2    C
2    C
Name: col1, dtype: object

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

Errors found:
	Errors in parameters section
		Parameters {'kwargs', 'args'} not documented
		Unknown parameters {'**kwargs', '*args'}
		Parameter "*args" has no type
		Parameter "**kwargs" has no type

```

The errors returned for the script is an error, since t is not ready for **kwargs and *args parameters.

@pedropazzini Can you check the similar PR https://github.com/pandas-dev/pandas/pull/19985 to see if there is something in there you can use? (eg explanation for the `**kwargs`) @pedropazzini Is there a reason that you closed this?