add threshold to config file

This is listed in the readme, but not in the actual published config

Author: mr-feek

config/config.php

@@ -6,6 +6,12 @@
      * If this is set to "null", the app.debug config value will be used.
      */
     'enabled' => env('QUERY_DETECTOR_ENABLED', null),
+    
+    /*
+     * Threshold level for the N+1 query detection. If a relation query will be
+     * executed more then this amount, the detector will notify you about it.
+     */
+    'threshold' => 1,
 
     /*
      * Here you can whitelist model relations.