Improve Backend comment. (#18567)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18567
ghimport-source-id: 1e50e611a3afcfae86828b7afe06c3fdc6a7bef7
Stack from [ghstack](https://github.com/ezyang/ghstack):
* **#18567 Improve Backend comment.**
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Reviewed By: dzhulgakov
Differential Revision: D14666189
fbshipit-source-id: 64a41c4a998b1a59ff780d1ae06fa16e5ef3c7c4
