[pkg] improve error message for module detection on saving pass (#73106)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/73106
The original error message didn't have next steps, and someone got confused. This error message should make debugging a bit easier.
Test Plan: Imported from OSS
Reviewed By: ngimel
Differential Revision: D34559499
Pulled By: PaliC
fbshipit-source-id: fd5fec9c4db10a20775435a587bad24336a671ef
(cherry picked from commit efdcf1e198389ee156a46cf0f8b185d8145d3266)
