Comment about UndergroundPathNorthSouth.blk size

Fixes pret#387

Author: Rangi42

constants/map_constants.asm

@@ -138,7 +138,7 @@ DEF FIRST_INDOOR_MAP EQU const_value
 	map_const UNUSED_MAP_74,                  0,  0 ; $74
 	map_const UNUSED_MAP_75,                  0,  0 ; $75
 	map_const HALL_OF_FAME,                   5,  4 ; $76
-	map_const UNDERGROUND_PATH_NORTH_SOUTH,   4, 24 ; $77
+	map_const UNDERGROUND_PATH_NORTH_SOUTH,   4, 24 ; $77 ; UndergroundPathNorthSouth.blk is actually 4x23
 	map_const CHAMPIONS_ROOM,                 4,  4 ; $78
 	map_const UNDERGROUND_PATH_WEST_EAST,    25,  4 ; $79
 	map_const CELADON_MART_1F,               10,  4 ; $7A