Document return locations.

include/item_menu.h

@@ -3,6 +3,20 @@
 
 #include "item.h"
 
+#define RETURN_LOCATION_FIELD 0
+#define RETURN_LOCATION_BATTLE 1
+#define RETURN_LOCATION_POKEMON_LIST 2
+#define RETURN_LOCATION_SHOP 3
+#define RETURN_LOCATION_FIELD_2 4
+#define RETURN_LOCATION_FIELD_3 5
+#define RETURN_LOCATION_PC 6
+#define RETURN_LOCATION_FIELD_4 7
+#define RETURN_LOCATION_FIELD_5 8
+#define RETURN_LOCATION_FIELD_6 9
+#define RETURN_LOCATION_BATTLE_2 10
+#define RETURN_LOCATION_PC_2 11
+#define RETURN_LOCATION_UNCHANGED 12
+
 // Exported type declarations
 struct BagStruct
 {