Added dot viewer to GUI screenshot overview

Author: joern274

documentation/hal_screenshot.html

@@ -69,6 +69,11 @@ <h1>HAL Screenshot</h1>
     <li><a href="https://github.com/emsec/hal/wiki/waveform-viewer-widget" target="_blank">Waveform Viewer</a></li>
     <li><a href="https://github.com/emsec/hal/wiki/python-console-widget" target="_blank">Python Console</a></li>
     <li><a href="https://github.com/emsec/hal/wiki/log-widget" target="_blank">Log Messages</a></li>
+    <li><a href="https://github.com/emsec/hal/wiki/dot-graph-viewer" target="_blank">Dot Graph Viewer</a></li>
   </ol></p>
+
+  <a href="https://github.com/emsec/hal/wiki/dot-graph-viewer" target="_blank">
+    <img src="https://raw.githubusercontent.com/emsec/hal/master/wiki_images/dot_viewer/widget.png"/>
+  </a>
 </body>
 </html>