DOC: Add documentation to __add__
- [x] closes #44784 
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [x] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [x] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.


I'm not sure what the convention on documenting (or not documenting) dunder methods is. If there's a better place to add documentation to resolve #44784 , happy to do that!
Thanks for your review @datapythonista ! 

Pushed a commit to update the example using animal names. Thanks for pointing that out!

To your initial question: I am not aware of any location where this docstring would get rendered the docs, because -- exactly to your point -- there doesn't seem to be a section for operators. Happy to either (a) add such a section (or subsection, etc.) to the docs or (b) relocate this documentation elsewhere, if either of those are desireable. Excellent. Thank you @datapythonista ! Pushed a few more commits to address your comments and added `__add__` to the docs. I'm going to start work on a reusable doc string for the other magic methods, pending comment from @MarcoGorelli . good one - thanks @jessica-writes-code !