README: Minor improvements (#56193)
Summary:
* Visual studio versions: clarify and shorten.
* Remove obsolete note about a bug that has been fixed.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56193
Reviewed By: albanD
Differential Revision: D27939766
Pulled By: ezyang
fbshipit-source-id: e142ec04ba98d5468f28ddf2e8bba5d99d3cfc26
