Describe the relation between fold and unfold operations. (#24840)
Summary:
Resolves https://github.com/pytorch/pytorch/issues/21817.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/24840
Differential Revision: D17113060
Pulled By: ezyang
fbshipit-source-id: 1f1a010d84582a943de7b1173c09e91fb0bd22ce
