chore: add gitter sidecar

Author: QingWei-Li

docs/index.html

@@ -87,6 +87,13 @@
   <script src="//unpkg.com/prismjs/components/prism-bash.min.js"></script>
   <script src="//unpkg.com/prismjs/components/prism-markdown.min.js"></script>
   <script src="//unpkg.com/prismjs/components/prism-nginx.min.js"></script>
+  
+  <script>
+  ((window.gitter = {}).chat = {}).options = {
+    room: 'docsifyjs/Lobby'
+  };
+  </script>
+  <script src="https://sidecar.gitter.im/dist/sidecar.v1.js" async defer></script>
 </body>
 
 </html>