title: Qt Creator and main window background image
body: <p>I would like to add an image as background of my main window.</p>
  
  <p>What is the best way to add this background image?</p>
  
  <p>The remaining part of my main window must be transparent.</p>
  
  <p>I would like to do this by <code>QtCreator</code> editor (for this component, therefore, no code)</p>