Suggest to add Game Over to documentation or to demo-disk.js

[djtanner]

Hi,
I just built my first text game using this awesome engine! One small feedback - it wasn't clear to me how to create a "game over" state like in the screenshot in the readme. I first did that only by generating a println statement once a certain action was done, but the game wasn't truly over because the player could still continue navigating. It only became clear to me once I found the unlimited-adventure.js file and saw that I should create a room with no exits for the game over state. (This also was by luck, as I was assuming "unlimited" meant there would not be a game over state!)

So I'd recommend adding how to achieve game over either to the readme or to all of the game disk demo files. I'm happy to do a PR for either option if you'd like.