Physical demo writeup

@kristjan The physical demo you did for this lesson was awesome. I'm speaking at the upcoming CoderDojo Conf. One of the things I want to talk about is the results that we've seen from using these physical demos. Since networking isn't really my area of skill, would you be willing to do a writeup of how the physical demo works? I'd like to actually have the audience of mentors try out the demo, but I'd love a script to refresh my memory of how it worked.

It would also be cool to include demos in lessons with step by step instructions of how to do them in case other dojos want to recreate them themselves. The whole talk is about getting the dojos to collaborate more, so it'd be awesome if I could link back to this repo and say "check out the script for the demonstration in the repo."