The entry point function of EnrollDefaultKeys finishes with a sanity check, verifying the values of the Secure Boot-related "control" variables. Add a diagram to explain why we expect the values we do. While at it, write comments on the rest of the entry point function. Cc: Anthony Perard <anthony.perard@citrix.com> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> Cc: Jordan Justen <jordan.l.justen@intel.com> Cc: Julien Grall <julien.grall@arm.com> Bugzilla: https://bugzilla.tianocore.org/show_bug.cgi?id=1747 Signed-off-by: Laszlo Ersek <lersek@redhat.com> Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com> Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Reviewed-by: Gary Lin <glin@suse.com>