Documentation/SubmittingPatches: suggested the use of scripts/get_maintainer.pl

Had I found a reference to scripts/get_maintainer.pl when I first read
Documentation/SubmittingPatches, it would've saved me some time.

Signed-off-by: Michel Machado <michel@digirati.com.br>
Acked-by: Rob Landley <rob@landley.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>