Update optim.rst for better understanding (#45944)
Summary:
The `i` variable in `Line 272` may cause ambiguity in understanding. I think it should be named as `epoch` variable.
Fixes #{issue number}
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45944
Reviewed By: agolynski
Differential Revision: D24219486
Pulled By: vincentqb
fbshipit-source-id: 2af0408594613e82a1a1b63971650cabde2b576e
