Add note about GPIO pin variations in wiring diagram (#537)

docs/docs/reference/diagram.mdx

@@ -16,6 +16,12 @@ Below you will find a wiring diagram of how everything is connected, depending o
   <img width="90%" src={require('@site/static/img/wiring_diagram.png').default} />
 </p>
 
+:::important
+Please note that there are different boards in circulation and that the GPIO
+pins may be on a different location than in the example above. So always double
+check and, if necessary, consult the pin layout of your specific board.
+:::
+
 ## GPIO pins
 
 In the tables below you will find more information, about how to connect the Photodiode PCB and the status LED.