README: Describe how Hoodie & Polymer provide an awesome sync experience

[timblack1]

Make this element's main selling point crystal clear, and provide example code to demonstrate.

Selling point

Hoodie syncs data between the server and JavaScript.

Polymer syncs data between JavaScript and the DOM.

(Illustrate with a graphic here.)

It's a match made in heaven.

It's two-way data binding all the way to the server, to other browsers, even to other users.

My data is your data, live.

Let the awesome begin.

Example code

(Make a model object which listens to a Polymer property's changes and syncs them to the server, and back again when changes are detected on the server. Make it easy to connect the two, maybe with something like this:

var model = new hoodie.PolymerModel(polymer_property, hoodie_id);

Or, consider making a plugin to Polymer's data-binding functionality to also automatically bind all properties to Hoodie there, if they are given a hoodie-type in their declaration.

Consider how to handle collections, or Polymer properties which contain more than one Hoodie doc. The firebase elements might be a good place to start: https://elements.polymer-project.org/elements/firebase-element.)