fix docs for lr (#28026)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28026
Documentation for learning rate does not render well. #27730.
Test Plan: Imported from OSS
Differential Revision: D17953395
Pulled By: vincentqb
fbshipit-source-id: 9e84df3e7de43f11399a67bc99c76ef241b1120f
