document reuse of variables in link mode

src/overworld.c

@@ -2908,6 +2908,9 @@ static void ZeroObjectEvent(struct ObjectEvent *objEvent)
     memset(objEvent, 0, sizeof(struct ObjectEvent));
 }
 
+// Note: Emerald reuses the direction and range variables during Link mode
+// as special gender and direction values. The types and placement
+// conflict with the usual Event Object struct, thus the definitions.
 #define linkGender(obj) obj->singleMovementActive
 // not even one can reference *byte* aligned bitfield members...
 #define linkDirection(obj) ((u8*)obj)[offsetof(typeof(*obj), fieldEffectSpriteId) - 1] // -> rangeX