boards: st: nucleo_h743zi: doc: add notice about board obsolescence

Important note to users about the obsolescence of NUCLEO_H743ZI.

Signed-off-by: Fabrice DJIATSA <[email protected]>

Author: djiatsaf-st

boards/st/nucleo_h743zi/doc/index.rst

@@ -43,6 +43,16 @@ Key Features
 
 More information about the board can be found at the `Nucleo H743ZI website`_.
 
+NUCLEO-H743ZI Board - Obsolescence Notice
+=========================================
+
+**Important Notice:** The NUCLEO-H743ZI development board is now **OBSOLETE** and
+no longer recommended for new designs or developments.
+STMicroelectronics has officially discontinued this product.
+As a result, we strongly advise all users to transition to the recommended replacement
+board: **NUCLEO-H753ZI**.
+For more information, please refer to the official STMicroelectronics product page `Nucleo H743ZI website`_.
+
 Hardware
 ********