docs: add `memory_format` in torch.empty (#54664)
Summary:
fixes https://github.com/pytorch/pytorch/issues/43504
Pull Request resolved: https://github.com/pytorch/pytorch/pull/54664
Reviewed By: ailzhang
Differential Revision: D27328504
Pulled By: zou3519
fbshipit-source-id: 6c3e11473ada34f7e9fae7bae366328e50f71b0e
