Migration doc fixes (#24033)
Summary:
This time I built the docs to make sure everything looks right
](https://our.intern.facebook.com/intern/diff/16719435/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/24033
Pulled By: driazati
Differential Revision: D16719435
fbshipit-source-id: 290c6431e7577ef9fbd595d9ac206df867366937
