added a main menu

scenes/mainmenu.gd

@@ -0,0 +1,13 @@
+extends Control
+
+# Called when the node enters the scene tree for the first time.
+func _ready():
+	pass # Replace with function body.
+
+# Called every frame. 'delta' is the elapsed time since the previous frame.
+func _process(delta):
+	pass
+
+
+func _on_start_game_btn_pressed():
+	print("start game!")