doc: Add documentation for STM32 MCUs

Add documentation for STM32 MCUs (F4, F7 and H7 series).

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
diff --git a/board/st/stm32h750-art-pi/MAINTAINERS b/board/st/stm32h750-art-pi/MAINTAINERS
index 9578833..2fd69e6 100644
--- a/board/st/stm32h750-art-pi/MAINTAINERS
+++ b/board/st/stm32h750-art-pi/MAINTAINERS
@@ -1,6 +1,7 @@
 STM32H750 ART PI BOARD
 M:	Dillon Min <dillon.minfei@gmail.com>
 S:	Maintained
+F:	doc/board/st/
 F:	board/st/stm32h750-art-pi
 F:	include/configs/stm32h750-art-pi.h
 F:	configs/stm32h750-art-pi_defconfig