Add loopback.social widget

Signed-off-by: Jung Hyun Nam <rkttu@rkttu.com>

Author: rkttu

_layouts/default.html

@@ -53,5 +53,6 @@ <h2 id="project_tagline">{{ site.description | default: site.github.project_tagl
       ga('send', 'pageview');
     </script>
   {% endif %}
+  <script src="https://loopback.social/banner.js" defer></script>
 </body>
 </html>