Update docs for cpp_extension on Windows (#30392)
Summary:
Targets https://github.com/pytorch/pytorch/issues/30379.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/30392
Differential Revision: D18730438
Pulled By: albanD
fbshipit-source-id: f718d006ee8aaaa356c1e15e53a0469f15e8ed41
