To persist data you'll want a backend. That's a fairly important piece of any application which is why I included it in the tutorial. You could ignore the Rails parts of the tutorial and create your own backend.
Maybe stub out the backend with an Express app? Express seems simple enough that even if you're not familiar with it, you can still understand what it's trying to do.
What's funny about that is that step is completely unnecessary. At least, I have never had to create a gemset and I have had up to 20 different Ruby applications on my machine at a time. Bundler solved this problem.
It's pretty tough to make a tutorial for literally everyone. Heck, some people use CoffeeScript and some use JavaScript, and any of them might be upset if your tutorial uses the other.
If someone wrote a plain Ember tutorial that just assumed the backend API already existed, just as many people might make the complaint "if you already have a backend, I'm sure this tutorial is just great, but for the rest of us..."
Perhaps I can just extract out the Ember portion -- It should still be applicable regardless of the backend.