Add more details to the known limitations section of torchhub docs (#69970)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/69970
This is a follow up to https://github.com/pytorch/hub/issues/243
Test Plan: Imported from OSS
Reviewed By: jbschlosser
Differential Revision: D33124060
Pulled By: NicolasHug
fbshipit-source-id: 298fe14b39a1aff3e0b029044c9a0db8bc82336a
