Add some more docs to expecttest. (#46263)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46263
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Test Plan: Imported from OSS
Reviewed By: robieta
Differential Revision: D24281640
Pulled By: ezyang
fbshipit-source-id: 88c5b3bf091f47b69ce58aa321669158c5afda79
