Made HOWTO a tiny bit better.

Documentation/HOWTO-change-firmware-and-compile-it_MeesElectronics.md

@@ -157,7 +157,17 @@ release-waveshare-esp32-s3-pico:
     rm -r build
 ```
 
-In the file Boards.h make an entry for the new board inside the '#if MCU_VARIANT == MCU_ESP32':
+The file `Board.h` is the most important file to edit. This is the place where the supported boards are defined. For our new board should, a new section has to be added.
+
+Search for the line `#if MCU_VARIANT == MCU_ESP32`. This is the part where all the ESP32 variant are defined. This section stops at the line `#elif MCU_VARIANT == MCU_NRF52`. From here the definitions for the NRF52 board begin.
+
+Somewhere between these to lines we have to add our board definition. It is good practice to add it at the end, just before the following code:
+
+    #else
+      #error An unsupported ESP32 board was selected. Cannot compile RNode firmware.
+    #endif
+
+Like so:
 
     // Board definition added by Mees Electronics
     #elif BOARD_MODEL == BOARD_WAVESHARE_ESP32_S3_PICO
@@ -207,6 +217,10 @@ In the file Boards.h make an entry for the new board inside the '#if MCU_VARIANT
           }
       };
 
+    #else
+      #error An unsupported ESP32 board was selected. Cannot compile RNode firmware.
+    #endif
+
 Also, in the file **Utilities.h** add entry. Again, inside the '#if MCU_VARIANT == MCU_ESP32'.
 
     	#elif BOARD_MODEL == BOARD_WAVESHARE_ESP32_S3_PICO