Update add-custom-route.rst

1. Change the namespace of the entity that manages the product from "RedKiteLabs\WebSiteBundle\Entity" to "Acme\WebSiteBundle\Entity"
2. Change 'AcmeWebSiteBundle:Product:product.html.twig' to 'AcmeWebSiteBundle:WebSite:product.html.twig' because Symfony2 uses a bundle:controller:template string syntax for templates.