Assemble technical overview of FX (#50291)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/50291
Test Plan: Imported from OSS
Reviewed By: pbelevich, SplitInfinity
Differential Revision: D25908444
Pulled By: ansley
fbshipit-source-id: 9860143a0b6aacbed3207228183829c18d10bfdb
