DOC: fix formatting in the ExtensionArray docstrings
- [x] closes #28685 
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Hello @HughKelley! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:



There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2019-10-14 21:05:31 UTC @datapythonista, seen above, there was an existing style error in the file modified for this pull request. Should I just go ahead and fix the line that is too long?  @datapythonista  
> 
> lgtm, thanks @HughKelley

First contribution to a project. Thanks for the help and direction! > First contribution to a project. Thanks for the help and direction!

You're welcome. Hopefully not the last one. :) @WillAyd thanks! Thanks @HughKelley 