Add comment about favicon cache busting

Author: rehandalal

public/index.html

@@ -9,6 +9,11 @@
       homescreen on Android. See https://developers.google.com/web/fundamentals/engage-and-retain/web-app-manifest/
     -->
     <link rel="manifest" href="%PUBLIC_URL%/manifest.json">
+    <!--
+      A `?v=<version>` has been appended to the end of the shortcut icon href
+      as a cache buster. 
+      </select>
+    -->
     <link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico?v=1">
     <!--
       Notice the use of %PUBLIC_URL% in the tags above.