Merge pull request docker#141 from mstanleyjones/choosing_port_vs_automatic

Fix incorrect information about swarm port assignment

Author: Misty Stanley-Jones

engine/swarm/key-concepts.md

@@ -74,7 +74,9 @@ run on the assigned node or fail.
 The swarm manager uses **ingress load balancing** to expose the services you
 want to make available externally to the swarm. The swarm manager can
 automatically assign the service a **PublishedPort** or you can configure a
-PublishedPort for the service in the 30000-32767 range.
+PublishedPort for the service. You can specify any unused port. If you do not
+specify a port, the swarm manager assigns the service a port in the 30000-32767
+range.
 
 External components, such as cloud load balancers, can access the service on the
 PublishedPort of any node in the cluster whether or not the node is currently