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 +1,23 @@
+:title: Port redirection
+:description: usage about port redirection
+:keywords: Usage, basic port, docker, documentation, examples
+
+
+Port redirection
+================
+
+Port redirection is done on ``docker run`` using the -p flag.
+
+Here are the 3 ways to redirect a port:
+
+.. code-block:: bash
+
+    # the port 80 in the container is mapped to a random port of the host
+    docker run -p 80 <image> <cmd>
+
+    # the port 80 in the container is mapped to the port 80 of the host
+    docker run -p :80 <image> <cmd>
+
+    # the port 80 in the container is mapped to the port 5555 of the host
+    docker run -p 5555:80 <image <cmd>
+