docs(installing_deis) add xip.io address for registering on EC2

closes #1126

Author: Octavian Geagla

docs/installing_deis/configure-dns.rst

@@ -11,6 +11,12 @@ You can use ``local.deisapp.com`` to both log into the controller and to access
 
 For Deis clusters hosted elsewhere (EC2, Rackspace, bare metal, etc.), DNS records will need to be created to point to the cluster. For a one-node cluster, we schedule and launch one router, and deis-router and deis-controller will run on the same host. So, the DNS record specified below can be configured to point to this one machine.
 
+If you do not modify your DNS settings on EC2 but still want to register a user, try using xip.io:
+
+.. code-block:: console
+
+    $ deis register deis.ec2-12-345-678-90.us-west-1.compute.amazonaws.com.xip.io
+
 On a multi-node cluster, however, there are probably multiple routers, and the controller will likely be scheduled on a separate machine. As mentioned in :ref:`configure-load-balancers`, a load balancer is recommended in this scenario.
 
 Note that the controller will eventually live behind the routers so that all external traffic will flow through the load balancer - configuring a DNS record which points to a service whose IP could change is less than ideal.