Add CosineAnnealingWarmRestarts to optim documentation (#25421)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/20028.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25421
Differential Revision: D17221542
Pulled By: soumith
fbshipit-source-id: 9c83c9ad6bf34ba59713c61485e4ef4b782a2792
