improve documentation of comparison internals (#68977)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/68977
Follow-up to #68722 to address the review comments that were left open before merge.
Test Plan: Imported from OSS
Reviewed By: ngimel
Differential Revision: D33542998
Pulled By: mruberry
fbshipit-source-id: 23c567cd328f83ae4df561ac8ee6c40c259408c9
