doc: you don't need Ultimate Edition IJ for the python plugin

This came up at Twitter build stand-up ~a week ago

Bugs closed: 848

Reviewed at https://rbcommons.com/s/twitter/r/1490/
Sync of https://github.com/pantsbuild/pants/commit/71c5363b5e9abcb9ed6e0a12ed8b61810de53c76