Update Documentation for Optionals (#16380)
Summary:
Now that https://github.com/pytorch/pytorch/pull/15587 has landed, updating docs.
Will close https://github.com/pytorch/pytorch/issues/15278
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16380
Differential Revision: D13825221
Pulled By: eellison
fbshipit-source-id: c5a7a7fbb40ba7be46a80760862468f2c9967169
