Updated README.md by correcting grammatical errors (#43779)
Summary:
Fixed grammatical errors and punctuation so that it be can more understandable.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43779
Reviewed By: ZolotukhinM
Differential Revision: D23407849
Pulled By: malfet
fbshipit-source-id: 09c064ce68d0f37f8023c2ecae8775fc00541a2c
