fix typo of quantized README.md (#50681)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/50681
Reviewed By: ngimel
Differential Revision: D25978905
Pulled By: jerryzh168
fbshipit-source-id: e8bff59a7a6b2b6f79273c010c32480db0997e7d
