DOC: updated docstring for deprecation of axis=1 in groupby
- [x] closes #54873
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.

@rhshadrach @mroeschke I added a note on the deprecation. Would be great if you could give some inputs here? Thanks @rsm-23 