Add digitalretro demo watchface

apps/imageclock/custom.html

@@ -18,6 +18,7 @@
     <button id="btnUpload" class="btn btn-primary">Upload to watch</button>
     <button id="btnSave" class="btn btn-secondary">Save resources file</button></br>
     <canvas id="canvas" style="display:none;"></canvas></br>
+    <p>Download Demo Watchface here: <a href="digitalretro.zip">digitalretro.zip</a></p>
 
     <script>     
       var result = "";