DOC: Updated docstring for Series.str.cat (pandas-dev#35556)
- [X] closes #35556
- [X] tests added / passed
- [X] passes `black pandas`
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

I have updated the docstring for `Series.str.cat` to make the issue in #35556 more explicit to the user.
I tried to figure out the cause of the two Azure pipeline tests failing, but could not understand how that would be caused by a change in the docstring.
I'd really appreciate some help or hints regarding this, thanks. Hi @souris-dev - this is off to a good start, if it's still active could you address Will's comments please? My apologies for the tardiness (was a bit busy the past week), I'll make the changes and commit in a day. Thanks. This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. Sorry for the delay, I'm in the process of addressing the comments and will update soon. Closing for now. @souris-dev let us know whenever you'd like to continue and we'll reopen!