Update help text to conform to style

- Clean up `temporal operator nexus` commands since they wrap beyond 80
  columns (and this would be visible to the user).
- Clarify wording on `temporal task-queue describe`, which was rather
  confusing in some places.

Both of these got scrutinized because they changed in the `nexus`
branch, but not in `main`, so they would not have been seen by our docs
folks.