MAINTAINERS: add doc/driver-model/ to DRIVER MODEL

The documentation should rest with the same maintainer as the code.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/MAINTAINERS b/MAINTAINERS
index 8add9d4..d1c4a28 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -607,6 +607,7 @@
 M:	Simon Glass <sjg@chromium.org>
 S:	Maintained
 T:	git https://gitlab.denx.de/u-boot/custodians/u-boot-dm.git
+F:	doc/driver-model/
 F:	drivers/core/
 F:	include/dm/
 F:	test/dm/