title: Adding custom images to nodes
body: <p>Using Sigma.js I want to add custom images to the graph's nodes. I found <a href="https://github.com/jacomyal/sigma.js/pull/106" rel="nofollow noreferrer">a plugin</a>, included nodeShapes.js and plotter.js, then added an image attribute :</p>
  
  <pre><code>var imgUri="somepicture.png"
  
  sigInst.addNode(id,{
                      'x': Math.random(),
                      'y': Math.random(),
                      'label': data.nodes[i].val,
                  //  'color': color,                         commenting this line out to add custom images to the nodes              
                      'image':{'url':imgUri},
                      'cluster': clusters['cluster_id']
  });
  </code></pre>
  
  <p>But the graph remains unchanged and I still see the default dots.</p>