title: Adding tooltip to an image
body: <p>Can't understand why my code isn't working, is there any way to display a tooltip on an image with extjs? </p>
  
  <pre><code>var img = Ext.create('Ext.Img', {
          src : 'img/ampoule.png',
          width : 30
  });
  
  var tip = Ext.create('Ext.tip.ToolTip', {
      target: img.getEl(),
      html: 'tooltip'
  });
  </code></pre>
  
  <p>My image is in the dockedItems of a treepanel like that :</p>
  
  <pre><code>dockedItems: [{
      xtype: 'toolbar',
      dock: 'top',
      items: [{
          fieldLabel: 'Search',
          /*****code code code everywhere*****/
          }
      ,
      img
     ]
  }]
  </code></pre>