Coccinelle: Update section of MAINTAINERS

Add Documentation/coccinelle.txt in the COCCINELLE section.
Signed-off-by: Nicolas Palix <nicolas.palix@imag.fr>
Signed-off-by: Michal Marek <mmarek@suse.cz>

MAINTAINERS

@@ -2103,6 +2103,7 @@ L:	cocci@systeme.lip6.fr (moderated for non-subscribers)
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild.git misc
 W:	http://coccinelle.lip6.fr/
 S:	Supported
+F:	Documentation/coccinelle.txt
 F:	scripts/coccinelle/
 F:	scripts/coccicheck