docs -mb2hal: make clear that the address has to be decimal integer (#2375)

Author: hansu

src/hal/user_comps/mb2hal/mb2hal_HOWTO.ini

@@ -93,7 +93,7 @@ SERIAL_DELAY_MS=10
 #Modbus slave number.
 MB_SLAVE_ID=1
 
-#REQUIRED: The first element address.
+#REQUIRED: The first element address (decimal integer).
 FIRST_ELEMENT=0
 
 #REQUIRED unless PIN_NAMES is specified: The number of elements.