[docs] gh-101273: Expand enum documentation on limitations

[samypr100]

Closes#101273

• Issue: Expand on enum limitations #101273

[ethanfurman]

I'm not sure this needs to be in the docs; I am sure that this is not the right section for them to be in. I'll try to review the enum docs this week to see if there is a better spot for this warning.

[samypr100]

@ethanfurman To expand a little on the motivation, the codebase that I originally encountered this had something close to

classElementType(StrEnum):
title="..."comment="..."author="..."# ...

It didn't occur to me at first that the errors I was seeing in mypy (mypy was being added after the fact) were due to StrEnum inheriting from str, hence why I also thought that it might be a good idea to add a warning/note to the docs.

[ethanfurman]

Closing in favor of #103596. Thank you, @samypr100 for the encouragement to properly fix this behavior.