Editing pass on native/README.md updates (#53638)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53638
Mostly slight edits, and deleting some outdated sections.
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Test Plan: Imported from OSS
Reviewed By: heitorschueroff
Differential Revision: D26920600
Pulled By: ezyang
fbshipit-source-id: e3bda80ecb622a1fcfde64e4752ba89a71056340
