Add GA to documentation

Author: nick-keller

package-lock.json

@@ -56,6 +56,9 @@ module.exports = {
         theme: {
           customCss: require.resolve('./src/css/custom.css'),
         },
+        gtag: {
+          trackingID: 'G-PZ8BTMNFN9',
+        },
       },
     ],
   ],