add port forwarding notes for mac/boot2docker docs

Docker-DCO-1.1-Signed-off-by: Cameron Boehmer <cameron.boehmer@gmail.com> (github: cameronboehmer)

docs/sources/installation/mac.rst

@@ -116,6 +116,21 @@ client just like any other application.
     # Git commit (server): c348c04
     # Go version (server): go1.2
 
+Forwarding VM Port Range to Host
+-------------------------------
+
+If we take the port range that docker uses by default with the -P option
+(49000-49900), and forward same range from host to vm, we'll be able to interact
+with our containers as if they were running locally:
+
+.. code-block:: bash
+
+   # vm must be powered off
+   for i in {4900..49900}; do
+    VBoxManage modifyvm "boot2docker-vm" --natpf1 "tcp-port$i,tcp,,$i,,$i";
+    VBoxManage modifyvm "boot2docker-vm" --natpf1 "udp-port$i,udp,,$i,,$i";
+   done
+
 SSH-ing The VM
 --------------