get_maintainer: --r (list reviewer) is on by default

We don't consistenly document the default value next to the option
listing, but we do have a list of defaults here, so let's keep it up to
date.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>