[PATCH master] Documentation: boards: stm32mp: elaborate on how to build

[Ahmad Fatoum]

The docs only show how to configure, not how to build the configuration.
Add the missing info to make this more evident.

Reported-by: https://stackoverflow.com/users/18074165/fila2016
Signed-off-by: Ahmad Fatoum <ahmad at a3f.at>
---
 Documentation/boards/stm32mp.rst | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Documentation/boards/stm32mp.rst b/Documentation/boards/stm32mp.rst
index 6f4b14049ad4..0c9615b290a5 100644
--- a/Documentation/boards/stm32mp.rst
+++ b/Documentation/boards/stm32mp.rst
@@ -28,7 +28,9 @@ Building barebox
 
 There's a single ``stm32mp_defconfig`` for all STM32MP boards::
 
-  make ARCH=arm stm32mp_defconfig
+  export ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf-
+  make stm32mp_defconfig
+  make
 
 The resulting images will be placed under ``images/``::
 
-- 
2.34.1