docs: Added Union to supported types in documentation (#68435)
Summary:
This PR simply updates the documentation following up on https://github.com/pytorch/pytorch/pull/64234, by adding `Union` as a supported type.
Any feedback is welcome!
cc ansley albanD gmagogsfm
Pull Request resolved: https://github.com/pytorch/pytorch/pull/68435
Reviewed By: davidberard98
Differential Revision: D32494271
Pulled By: ansley
fbshipit-source-id: c3e4806d8632e1513257f0295568a20f92dea297
