Fix DDP docs (#45454)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/45454
Test Plan: Imported from OSS
Reviewed By: pritamdamania87
Differential Revision: D23973367
Pulled By: mrshenli
fbshipit-source-id: 11f20d51d0d0f92f199e4023f02b86623867bae0
