Updated config documentation

ampel-firmware/config.public.h

@@ -59,10 +59,10 @@
  */
 
 // LED brightness, which can vary between min and max brightness ("LED breathing")
-// MAX_BRIGHTNESS should be between 0 and 255.
+// MAX_BRIGHTNESS must be defined, and should be between 0 and 255.
 #  define MAX_BRIGHTNESS 255
-// MIN_BRIGHTNESS should be between 0 and MAX_BRIGHTNESS - 1
-// If MIN_BRIGHTNESS is not set, or set to MAX_BRIGHTNESS, breathing is disabled.
+// MIN_BRIGHTNESS, if defined, should be between 0 and MAX_BRIGHTNESS - 1
+// If MIN_BRIGHTNESS is not set, or if it is set to MAX_BRIGHTNESS, breathing is disabled.
 #  define MIN_BRIGHTNESS 60
 
 /**