Add links to more subdir READMEs in CONTRIBUTING.md (#38049)
Summary:
I think it would be nice to have these extra README links here so they're easier to find. There are even more READMEs throughout the source tree that I didn't include, but most of them seem to have pretty minimal information.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38049
Differential Revision: D21470749
Pulled By: ezyang
fbshipit-source-id: aa164a3776ab90f2453634082eeae20c0dd002ce
