Update document.html

Author: riverfor

docs/document.html

@@ -273,5 +273,14 @@ <h2>For Chinese users<a class="headerlink" href="#for-chinese-users" title="Perm
       }
     })
   </script>
+	  <!-- Google tag (gtag.js) -->
+<script async src="https://www.googletagmanager.com/gtag/js?id=G-3GZ8CTQYNC"></script>
+<script>
+  window.dataLayer = window.dataLayer || [];
+  function gtag(){dataLayer.push(arguments);}
+  gtag('js', new Date());
+
+  gtag('config', 'G-3GZ8CTQYNC');
+</script>
   </body>
 </html>