Added the missing config to use new terrains (#5792)

Co-authored-by: Hedara <[email protected]>

include/config/battle.h

@@ -219,6 +219,7 @@
 #define B_SECRET_POWER_ANIMATION    GEN_LATEST // Secret Power's animations change depending on terrain and generation.
 #define B_NATURE_POWER_MOVES        GEN_LATEST // Nature Power calls different moves depending on terrain and generation. See sNaturePowerMoves.
 #define B_CAMOUFLAGE_TYPES          GEN_LATEST // Camouflage changes the user to different types depending on terrain and generation. See sTerrainToType.
+#define B_NEW_TERRAIN_BACKGROUNDS   FALSE      // If set to TRUE, uses new terrain backgrounds for Electric, Misty, Grassy and Psychic Terrain.
 
 // Interface settings
 #define B_ABILITY_POP_UP            TRUE  // In Gen5+, the Pokémon abilities are displayed in a pop-up, when they activate in battle.