Add some note about SF Bundle & Flex

Author: lyrixx

README.md

@@ -1,6 +1,9 @@
 # OpenApi Bundle
 
 The component ships a Bundle to allow a quick integration with Symfony for the OpenApiCommon component of Jane.
+
+**Note**: If you use Symfony Flex, the configuration is automatic
+
 To use it, you just have to add the main bundle class to your `config/bundles.php` file.
 ```
 return [