Add codeowners for functorch (#86213)
The list is for people who want to be notified on changes to the files
in there. Review is not required from the list of names; I just want to be
notified to keep track of what is going on.
Let me know if you want your names added too in this PR.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/86213
Approved by: https://github.com/Chillee
