update readme

README.md

@@ -71,12 +71,15 @@ Searching for a phrase or keyword is trivial
 
     $res = $tnt->search("This is a test search", 12);
 
-    print_r($res); //returns 12 document ids that best match your query
+    print_r($res); //returns an array of 12 document ids that best match your query
 
     //to display the results you need an aditional query
-    //SELECT * FROM articles WHERE id IN $res;
+    //SELECT * FROM articles WHERE id IN $res ORDER BY FIELD(id, $res);
 ```
 
+The ORDER BY FIELD clause is important otherwise the database engine will not return
+the results in required order
+
 ## Contributing
 
 Please see [CONTRIBUTING](CONTRIBUTING.md) and [CONDUCT](CONDUCT.md) for details.