Document berry yield

fix wording

include/berry.h

@@ -1,6 +1,8 @@
 #ifndef GUARD_BERRY_H
 #define GUARD_BERRY_H
 
+#define NUM_BERRY_STAGES 4
+
 void ClearEnigmaBerries(void);
 void SetEnigmaBerry(u8 *src);
 bool32 IsEnigmaBerryValid(void);