title: How to set background from image file in pygtk+ 3
body: <p>How to set background from image file in pygtk+ 3 ?
  I tried with this but all the rest items in the application goes above it or below the image. I can change the bg colour with Gdk, but I want to see my custom made image in the background of the application.</p>
  
  <pre><code>image = Gtk.Image()
  image.set_from_file("image.png")
  self.add(image)
  </code></pre>