DOC: add python 3.10 support to docs

[Dr-Irv]

Pandas version checks

• I have checked that the issue still exists on the latest versions of the docs on main here

Location of the documentation

https://pandas.pydata.org/docs/dev/getting_started/install.html

Documentation problem

Need to update this page to say that python 3.10 is now supported.

Suggested fix for documentation

Add python 3.10 to the supported python versions.