Fix documentation preview instructions (#61080)
Summary:
People don't need to self host these anymore since we do it automatically in PRs
Pull Request resolved: https://github.com/pytorch/pytorch/pull/61080
Reviewed By: VitalyFedyunin, janeyx99
Differential Revision: D29506465
Pulled By: driazati
fbshipit-source-id: 45875cb229f8cc565a9a1405f52cef198ee0e687
