Add Google tag for analytics tracking

Author: xuelink

index.html

@@ -392,5 +392,20 @@ <h1>langX<br /></h1>
         });
       });
     </script>
+
+    <!-- Google tag (gtag.js) -->
+    <script
+      async
+      src="https://www.googletagmanager.com/gtag/js?id=G-KXRC5YCB27"
+    ></script>
+    <script>
+      window.dataLayer = window.dataLayer || [];
+      function gtag() {
+        dataLayer.push(arguments);
+      }
+      gtag("js", new Date());
+
+      gtag("config", "G-KXRC5YCB27");
+    </script>
   </body>
 </html>