Document FX debugging (#51530)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/51530
Test Plan: Imported from OSS
Reviewed By: jamesr66a
Differential Revision: D26192641
Pulled By: ansley
fbshipit-source-id: c69ab1bb2451d8ee5a729445f52bccc66e6f431b
