Convert readthedocs link for their .org -> .io migration for hosted projects

Convert readthedocs link for their .org -> .io migration for hosted projects

As per their email ‘Changes to project subdomains’:

> Starting today, Read the Docs will start hosting projects from subdomains on the domain readthedocs.io, instead of on readthedocs.org. This change addresses some security concerns around site cookies while hosting user generated data on the same domain as our dashboard.

Test Plan: Manually visited all the links I’ve modified.

(cherry picked from commit 513a045395b4cb5d8e1a9deb69bc9761d79eee37)