toradex: MAINTAINERS: entries for new reST docs

Add entries for the newly created documentation files in reST
format.

Signed-off-by: Igor Opaniuk <igor.opaniuk@toradex.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/board/toradex/verdin-imx8mm/MAINTAINERS b/board/toradex/verdin-imx8mm/MAINTAINERS
index 3b4fae5..2495696 100644
--- a/board/toradex/verdin-imx8mm/MAINTAINERS
+++ b/board/toradex/verdin-imx8mm/MAINTAINERS
@@ -6,4 +6,5 @@
 F:	arch/arm/dts/imx8mm-verdin-u-boot.dtsi
 F:	board/toradex/verdin-imx8mm/
 F:	configs/verdin-imx8mm_defconfig
+F:	doc/board/toradex/verdin-imx8mm.rst
 F:	include/configs/verdin-imx8mm.h