title: adding submenu in pyqt QWidget
body: <p>I know its very basic question but I am little bit confused, probably I am forgetting something.</p>
  
  <p>I am trying to add a sub menu "Preview" to the "Tools" in the QMenuBar() </p>
  
  <p>so far this is what I am trying to do </p>
  
  <pre><code>tools = fileMenu.addMenu('&amp;Tools')
  prevAction = QtGui.QAction('Preview',self)
  prevInNuke = QtGui.QAction("Using &amp;Nuke",prevAction)
  tools.addAction(prevAction)
  prevAction.addAction(prevInNuke)
  </code></pre>
  
  <p>but I guess this is not the correct way to add a sub menu </p>