[learnability] Add a status message teaching commit on Deferred Sheet

The commit keystroke is different from the standard save, and is not-intuitive.

This can result in confusion where users do not know how to propagate their changes.

In Emacs dired-mode, when you enter the wdired minor mode (where you can interactively rename files) it shows a message at the bottom saying "Press C-c C-c when finished or C-c ESC to abort changes"

This seems like a useful status message or wizard to be added.