rework migration section to show existing entities

Author: hackzilla

README.md

@@ -50,8 +50,6 @@ TicketBundle show fires events for creating, updating, and deleting of tickets.
 See for example of how to create listener: http://symfony.com/doc/current/cookbook/service_container/event_listener.html
 
 
-## Migration from v2 to v3
-
 Add your user, ticket and ticket message entities into your config.
 
 ```yaml
@@ -69,8 +67,18 @@ Your entities  needs to implement:
 | Ticket | ```Hackzilla\Bundle\TicketBundle\Model\MessageInterface``` |
 | Message | ```Hackzilla\Bundle\TicketBundle\Model\TicketMessageInterface``` |
 
-Any reference to TicketMessage constants will need to use TicketMessageInterface.
+## Migration from v2 to v3
+
+Ticket and TicketMessage entities still exist and the config will default to them if not overridden.
 
+```yaml
+hackzilla_ticket:
+    user_class:             AppBundle\Entity\User
+    ticket_class:           Hackzilla\Bundle\TicketBundle\Entity\Ticket
+    message_class:          Hackzilla\Bundle\TicketBundle\Entity\TicketMessage
+```
+
+Any reference to TicketMessage constants will need to use TicketMessageInterface.
 
 ## Migrating from v1 to v2