Update intro doc for derivatives.yaml (#60614)
Summary:
Clarify some phrasing and document the findings on the different non differentiable states.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/60614
Reviewed By: anjali411
Differential Revision: D29362740
Pulled By: albanD
fbshipit-source-id: 5bc2e8b8dde57ba5a9247d7c28b83c793703e35f
