Revert "Revert D21337640: [pytorch][PR] Split up documentation into subpages and clean up some warnings" (#37778)
Summary:
Original PR: https://github.com/pytorch/pytorch/pull/37419
cc mattip suo
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37778
Differential Revision: D21385774
Pulled By: ezyang
fbshipit-source-id: 5de532faab8bae132736b6b5189e0ee2ac9935be
