Update to Prelude

I took a shot at trying to give the opening few paragraphs of the Prelude more punch per Jeremy's request in #342. Feel free to use or not - it may not even be accurate given my dearth of client-side development experience prior to using Backbone!

I think it may still lack the exposition that Jeremy is looking for (in terms of a specific example), but I think that is better left to being addressed in the introduction.