add a note to reuse existing fields

Author: milaGGL

packages/firestore/test/integration/api/composite_index_query.test.ts

@@ -45,6 +45,10 @@ import { apiDescribe } from '../util/helpers';
  * To get started, please refer to the instructions provided in the README file. This will guide you
  * through setting up your local testing environment and updating the Terraform configuration with
  * any new composite indexes required for your testing scenarios.
+ * 
+ * Note: Whenever feasible, make use of the current document fields (such as 'a,' 'b,' 'author,'
+ * 'title') to avoid introducing new composite indexes and surpassing the limit. Refer to the
+ * guidelines at https://firebase.google.com/docs/firestore/quotas#indexes for further information.
  */
 apiDescribe('Composite Index Queries', persistence => {
   // OR Query tests only run when the SDK's local cache is configured to use