Merge pull request #911 from dotcloud/add_port_redirection_doc

* Documentation: add port redirection doc

docs/sources/use/index.rst

@@ -14,6 +14,7 @@ Contents:
 
    basics
    workingwithrepository
+   port_redirection
    builder
    puppet
 

docs/sources/use/port_redirection.rst

@@ -0,0 +1,25 @@
+:title: Port redirection
+:description: usage about port redirection
+:keywords: Usage, basic port, docker, documentation, examples
+
+
+Port redirection
+================
+
+Docker can redirect public tcp ports to your container, so it can be reached over the network.
+Port redirection is done on ``docker run`` using the -p flag.
+
+A port redirect is specified as PUBLIC:PRIVATE, where tcp port PUBLIC will be redirected to
+tcp port PRIVATE. As a special case, the public port can be omitted, in which case a random
+public port will be allocated.
+
+.. code-block:: bash
+
+    # A random PUBLIC port is redirected to PRIVATE port 80 on the container
+    docker run -p 80 <image> <cmd>
+
+    # PUBLIC port 80 is redirected to PRIVATE port 80
+    docker run -p 80:80 <image> <cmd>
+
+
+Default port redirects can be built into a container with the EXPOSE build command.