Updated SGD docs with subscripts (#23985)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/23982
Obvious improvement imo.
Also changed `rho` to `mu`, since `rho` and `p` look very similar.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23985
Differential Revision: D16733037
Pulled By: Chillee
fbshipit-source-id: 5431615d1983f24d6582da6fc8103ac0093b5832
