Fix README for installation from source (#37301)
Summary:
I think, it's help faster compile pytorch from source without errors about incompatible compiler(such as: unsupported GNU version! gcc versions later than 8 are not supported!)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37301
Differential Revision: D21396682
Pulled By: ngimel
fbshipit-source-id: 5e21c36ee550424e820f3aa6e6131ca858994ae4
