add welcome menu

Assets/Prefabs/Menu.prefab

@@ -1357,7 +1357,7 @@ MonoBehaviour:
   m_EditorClassIdentifier: 
   themeSelector: {fileID: 7285044980238930537}
   data:
-    themeIndex: 3
+    themeIndex: 4
 --- !u!1 &5305278009141335879
 GameObject:
   m_ObjectHideFlags: 0
@@ -1574,7 +1574,7 @@ Canvas:
   m_GameObject: {fileID: 5305278010342315831}
   m_Enabled: 1
   serializedVersion: 3
-  m_RenderMode: 0
+  m_RenderMode: 1
   m_Camera: {fileID: 0}
   m_PlaneDistance: 100
   m_PixelPerfect: 0