DOC: add 'pandas ecosystem' section to docs
cc @jseabold, @glamp, @mwaskom, @kjordahl, @wrobstory

Feel free to suggest a better blurb if you'd like.

Replaces the `related libraries` section, which I feel is outdated.

closes #5804

:+1:
 nice!

maybe add a small addendum on create the next release setup

e.g. adding section in release notes / whatsnew / setting the new release nums?
 sure, just add it to the wiki page.
