Updated "Use -> The Basics" to use ubuntu:12.10.

ubuntu:latest doesn't have nc. ubuntu:12.10 does.

docs/sources/use/basics.rst

@@ -142,7 +142,7 @@ Expose a service on a TCP port
 .. code-block:: bash
 
   # Expose port 4444 of this container, and tell netcat to listen on it
-  JOB=$(sudo docker run -d -p 4444 ubuntu /bin/nc -l -p 4444)
+  JOB=$(sudo docker run -d -p 4444 ubuntu:12.10 /bin/nc -l -p 4444)
 
   # Which public port is NATed to my container?
   PORT=$(sudo docker port $JOB 4444)