MAINTAINERS: put docs/man/ under tool stack

Right now there's only tool stack related documentation there.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- unstable.orig/MAINTAINERS
+++ unstable/MAINTAINERS
@@ -353,6 +353,7 @@ F:	install.sh
 F:	m4/
 F:	configure
 F:	docs/Makefile
+F:	docs/man/
 F:	stubdom/Makefile
 F:	*.ac
 F:	*/configure