title: Add SCNText to SCNPlane
body: <p>i am adding an SCNPlane using </p>
  
  <pre><code>artPlane = SCNPlane(width: CGFloat(widthRequired) * 0.0254,
                          height: CGFloat(size["width"]!) * 0.0254)
  
      artworkNode = SCNNode(geometry: artPlane)
  
      artworkNode?.geometry?.firstMaterial?.diffuse.contents = UIImage(named: "loadingar")
  
      let translation = SCNMatrix4MakeTranslation(0, -1, 0)
      let rotation = SCNMatrix4MakeRotation(Float.pi / 2, 0, 0, 1)
      artworkNode?.geometry?.firstMaterial?.diffuse.contentsTransform = SCNMatrix4Mult(translation, rotation)
  
      artworkNode?.geometry?.firstMaterial?.isDoubleSided = true
      artworkNode?.simdTransform = matrix
  
      self.sceneView.scene.rootNode.addChildNode(artworkNode!)
  </code></pre>
  
  <p>Now i want to add an SCNText to the center of the above plane, how do i specify the position of the new textNode so that its in the center of the Plane?</p>