Fixed the comment to reference gist example instead of private repo (#18852)
Summary:
Replace link to a file in a private repo with a gist
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18852
Reviewed By: ezyang
Differential Revision: D14778481
Pulled By: izdeby
fbshipit-source-id: 8389aa4bf115ddcfd85079cc2c861404efa678e7
