Add ssh port forwarding steps to EC2 dev setup instructions

Author: davidsbailey

SETUP.md

@@ -178,6 +178,9 @@ Many Windows developers have found that setting up an Ubuntu virtual machine is
        ```
      * run `ssh yourname-ec2` to connect to your instance
   1. Go back up to the [overview](#overview) and run the commands there.
+  1. Once you have successfully completed `rake build`, you can connect to it as follows:
+     * run `ssh -L 3000:127.0.0.1:3000 yourname-ec2 ~/code-dot-org/bin/dashboard-server` on your local machine. This sets up SSH port forwarding from your local machine to your ec2 dev instance for as long as your dashboard server is running.
+     * navigate to http://localhost-studio.code.org:3000/ on your local machine
 
 ## Enabling JavaScript builds
 The default dashboard install uses a static build of JS, but if you want to make modifications to these you'll want to enable local builds of the JavaScript packages. You'll need to do this once: