add linked containers to hosts file

Docker-DCO-1.1-Signed-off-by: Bryan Murphy <bmurphy1976@gmail.com> (github: bmurphy1976)

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Tested-by: Solomon Hykes <solomon@docker.com> (github: shykes)

docs/sources/reference/run.md

@@ -1,4 +1,4 @@
-page_title: Docker Run Reference 
+page_title: Docker Run Reference
 page_description: Configure containers at runtime
 page_keywords: docker, run, configure, runtime
 
@@ -407,6 +407,13 @@ And we can use that information to connect from another container as a client:
     $ docker run -i -t --rm --link redis-name:redis_alias --entrypoint /bin/bash dockerfiles/redis -c '/redis-stable/src/redis-cli -h $REDIS_ALIAS_PORT_6379_TCP_ADDR -p $REDIS_ALIAS_PORT_6379_TCP_PORT'
     172.17.0.32:6379>
 
+Docker will also map the private IP address to the alias of a linked
+container by inserting an entry into `/etc/hosts`.  You can use this
+mechanism to communicate with a linked container by its alias:
+
+    $ docker run -d --name servicename busybox sleep 30
+    $ docker run -i -t --link servicename:servicealias busybox ping -c 1 servicealias
+
 ## VOLUME (Shared Filesystems)
 
     -v=[]: Create a bind mount with: [host-dir]:[container-dir]:[rw|ro].