added cut as method to Series
- [x] closes #28925 
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Not sure if we need to totally re-implement cut. Please feel free to give any advice, I am new to contributing.
Hello @R4HMATT! Thanks for opening this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:

* In the file [`pandas/core/series.py`](https://github.com/pandas-dev/pandas/blob/a1a2dbb0c5f846028515dccf6b1db8748e3a5244/pandas/core/series.py):

> [Line 4529:5](https://github.com/pandas-dev/pandas/blob/a1a2dbb0c5f846028515dccf6b1db8748e3a5244/pandas/core/series.py#L4529): [E303](https://duckduckgo.com/?q=pep8%20E303) too many blank lines (2)
> [Line 4539:49](https://github.com/pandas-dev/pandas/blob/a1a2dbb0c5f846028515dccf6b1db8748e3a5244/pandas/core/series.py#L4539): [W291](https://duckduckgo.com/?q=pep8%20W291) trailing whitespace
> [Line 4540:1](https://github.com/pandas-dev/pandas/blob/a1a2dbb0c5f846028515dccf6b1db8748e3a5244/pandas/core/series.py#L4540): [W293](https://duckduckgo.com/?q=pep8%20W293) blank line contains whitespace
> [Line 4550:13](https://github.com/pandas-dev/pandas/blob/a1a2dbb0c5f846028515dccf6b1db8748e3a5244/pandas/core/series.py#L4550): [E123](https://duckduckgo.com/?q=pep8%20E123) closing bracket does not match indentation of opening bracket's line

 Thanks for the PR. Why do you think this is a good idea though? Echoing @WillAyd and my https://github.com/pandas-dev/pandas/issues/28925#issuecomment-541977217, I am still not convinced adding cut as a Series method makes sense. Not sure if you are referring to the implementation or for the feature itself.

For the feature itself, the original issue expressed better method chaining for series like so:
`df.some_series.fillna(0).cut(10).mean()`.

At the moment, the above can only be done like this:
```
filled_series = df.some_series.fillna(0)
pd.cut(filled_series, 10).mean()
``` Series is only 1 possible output from `cut` that can be chained with other methods.

`cut` can otherwise produce a `Categorical`, `tuple`, or `ndarray` that cannot be chained. @mroeschke Would it make sense (or even possible) to force the Series method implementation of cut to only return another Series objects then? Possibly, but making the output behavior of `pd.cut` inconsistent with `Series.cut` would be odd from an API perspective.

Also for chaining, one can always call `Series.apply(pd.cut)` Thanks for your interest in contributing @R4HMATT. I think there needs to be more discussion from the community plus core developers on the original issue before starting a PR for this feature. 

Feel free to contribute to many of the other issues!