More detailed docs on using non-AMD assets with ember-cli

Not having worked with javascript dependencies before, I found the current ember-cli docs confusing since they spoke of the admittedly amazing ES6 imports, except that they aren't available yet!

Hopefully this will clarify for other noobs how to handle dependencies immediately.
moment actually has AMD, and is something we will soon support, as leaf supports it: https://github.com/stefanpenner/leaf/blob/master/tests/moment-test.js