Refine CosineAnnealingWarmRestarts doc for issue #20028 (#20267)
Summary:
Fixes #20028
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20267
Differential Revision: D15393514
Pulled By: ezyang
fbshipit-source-id: 03f270a577fc3e0414d3f07d97512a409b08f7cd
