title: How do I create a HUD on top of my Scenekit.scene
body: <p>I'm experimenting with Swift and Scenekit.
  Building a Mac OS X app.
  It seems quite easy to get a 3d-scene working.
  But what is scene without some kind of 2D hi-score, radar display, speed indicator, etc?
  I would expect a SpriteKit-scene to seamlessly integrate into a SceneView but I don't find the documentation very clear about this..</p>
  
  <p>The most obvious and only way I can think of is to position a SKView over a SceneView and render each separately.
  But is there a more elegant way?</p>