* Add instructions to the workflow at the point where the failure would
occur, which is where someone experiencing a failure is most likely to
look. To keep things simple, the instructions are always printed. The
assumption is that if the job succeeds, nobody is likely to look
anyway.
* Provides the diff of the failure as an artifact, so the user can apply
it directly to their repo.
* Also update the levelization/README.md to clarify the levels a little
bit.
