Update README.md

Co-authored-by: Barry Pollard <barrypollard@google.com>

README.md

@@ -376,7 +376,8 @@ function sendToGoogleAnalytics({name, delta, id}) {
     // OPTIONAL: any additional attribution params here.
     // See: https://web.dev/debug-web-vitals-in-the-field/
     // metric_rating: 'good' | 'ni' | 'poor',
-    // debug_info: '...',
+    // dimension1: '...',
+    // dimension2: '...',
     // ...
   });
 }