[docs] Add images to some activation functions (#65415)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/65368. See discussion in the issue.
cc mruberry SsnL jbschlosser soulitzer
Pull Request resolved: https://github.com/pytorch/pytorch/pull/65415
Reviewed By: soulitzer
Differential Revision: D31093303
Pulled By: albanD
fbshipit-source-id: 621c74c7a2aceee95e3d3b708c7f1a1d59e59b93
