Document item use

include/constants/items.h

@@ -448,6 +448,11 @@
 #define NUM_TECHNICAL_MACHINES 50
 #define NUM_HIDDEN_MACHINES     8
 
+// Secondary IDs for rods
+#define OLD_ROD   0
+#define GOOD_ROD  1
+#define SUPER_ROD 2
+
 // Check if the item is one that can be used on a Pokemon.
 #define IS_POKEMON_ITEM(item) ((item) >= ITEM_POTION && (item) <= ITEM_0B2)