Add some sounds

scripts/power_station.gd

@@ -32,4 +32,9 @@ func collect_charges_from_station():
 
 func _on_coin_machine_coin_requirement_met(player):
 	assert(player.has_method("modify_inventory"))
-	player.modify_inventory("coins", collect_charges_from_station())
+	var charges = collect_charges_from_station()
+	player.modify_inventory("coins", charges)
+	if charges > 0:
+		$sounds/charge_get.play()
+	else:
+		$sounds/error.play()