Add gitter chatting room

docs/_layouts/default.html

@@ -37,6 +37,12 @@
         })(window,document,'script','dataLayer','GTM-PCLWNCD');
         </script>
         <!-- End Google Tag Manager -->
+        <script>
+            ((window.gitter = {}).chat = {}).options = {
+                room: 'SpaceVim/SpaceVim'
+            };
+        </script>
+        <script src="https://sidecar.gitter.im/dist/sidecar.v1.js" async defer></script>
         <meta charset="utf-8">
         <meta http-equiv="X-UA-Compatible" content="chrome=1">
         <title>{{ page.title | default: Home }} - SpaceVim</title>