Improve `nn.Sequential` documentation (#53380)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/53380
Test Plan: Imported from OSS
Reviewed By: nikithamalgifb
Differential Revision: D26849861
Pulled By: ansley
fbshipit-source-id: 2add8c73ae421332ed1c03340806e25656bafabb
