Revised sparse tensor documentation. (#45400)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/44635.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45400
Reviewed By: ezyang
Differential Revision: D24359410
Pulled By: mruberry
fbshipit-source-id: 37c691a49a7b0042c7a298e0ed1226702b097c8b
