Update README.md

Author: tuyakhov

README.md

@@ -92,6 +92,29 @@ class Article extends ActiveRecord implements ResourceInterface
   }
 }
 ```
+Controlling JSON API output
+------------------------------
+The JSON response is generated by the `tuyakhov\jsonapi\JsonApiResponseFormatter` class which will
+use the `yii\helpers\Json` helper internally. This formatter can be configured with different options like
+for example the `$prettyPrint` option, which is useful on development for
+better readable responses, or `$encodeOptions` to control the output
+of the JSON encoding.
+
+The formatter can be configured in the `yii\web\Response::formatters` property of the `response` application
+component in the application configuration like the following:
+
+```php
+'response' => [
+    // ...
+    'formatters' => [
+        \yii\web\Response::FORMAT_JSON => [
+            'class' => 'tuyakhov\jsonapi\JsonApiResponseFormatter',
+            'prettyPrint' => YII_DEBUG, // use "pretty" output in debug mode
+            'encodeOptions' => JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE,
+        ],
+    ],
+],
+```
 Enabling JSON Input
 ---------------------------
 To let the API accept input data in JSON API format, configure the [[yii\web\Request::$parsers|parsers]] property of the request application component to use the [[tuyakhov\jsonapi\JsonApiParser]] for JSON input