MAINTAINERS: list openvswitch docs under its entry

Submissions to the docs seem to not get properly CCed.

Acked-by: Ilya Maximets <i.maximets@ovn.org>
Link: https://patch.msgid.link/20250202005024.964262-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

MAINTAINERS

@@ -17706,6 +17706,7 @@ L:	netdev@vger.kernel.org
 L:	dev@openvswitch.org
 S:	Maintained
 W:	http://openvswitch.org
+F:	Documentation/networking/openvswitch.rst
 F:	include/uapi/linux/openvswitch.h
 F:	net/openvswitch/
 F:	tools/testing/selftests/net/openvswitch/