Document example of Proxy use (#50583)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/50583
Test Plan: Imported from OSS
Reviewed By: pbelevich
Differential Revision: D26010501
Pulled By: ansley
fbshipit-source-id: 947121af7e57c16c96f849fbbb3fa83e97d003b2
