Add source code link

tutorials/device-dashboard/web_root/index.html

@@ -134,7 +134,8 @@
           </article>
           <article class="metric-tile note" style="min-width: 15rem;">
             <div>
-            To tailor this dashboard to your firmware, follow
+              This dashboard source code is <a href="https://github.com/cesanta/mongoose/tree/master/tutorials/device-dashboard" target="_blank">here</a>.
+              To tailor it to your firmware, follow
               <a target="_blank" href="https://mongoose.ws/docs/guides/web-dashboard-guide/#dashboard-example">this guide</a>
             </div>
           </article>