Add documentation for [JS-SDK] ParseQuery.withCount

_includes/js/queries.md

@@ -57,6 +57,25 @@ You can skip the first results by setting `skip`. In the old Parse hosted backen
 query.skip(10); // skip the first 10 results
 ```
 
+If you want to know the total number of rows in table satisfying your query, for  e.g. pagination purposes - you can use `withCount` (`false` by default). **Note** Enabling this flag will change the structure of response, see example below.
+
+Let's say you have 200 rows in `GameScore` table:
+
+```javascript
+const GameScore = Parse.Object.extend("GameScore");
+const query = new Parse.Query(GameScore);
+
+query.limit(25);
+
+const results = await query.find(); // [ GameScore, GameScore, ...]
+
+// to include count:
+query.withCount(true);
+const response = await query.find(); // { results: [ GameScore, ... ], count: 200 }
+```
+⚠️ Сount operations can be slow and expensive.
+> If you only want to get the count without objects - use [Counting Objects](#counting-objects).
+
 For sortable types like numbers and strings, you can control the order in which results are returned:
 
 ```javascript