add explanation

src/screens/app_gui.h

@@ -79,7 +79,7 @@ struct State {
   uint16_t moisture_raw;
   uint16_t moisture_pt;
   struct rtc_time last_cycle_time;
-  bool cycle_time_checking; // TODO unclear what this does???
+  bool cycle_time_checking; // This is used to prevent cycle being started again and again during the same minute - it is cleared once the HH:MM time changes.
 
   /// Repaint was requested from the screen code
   bool paint_needed;