Add a screen grab of the UI to the readme

[brianboyer]

We're still not really selling it.

Also, maybe a better description: "Quotable is a little website that helps you make images from quotations. Paste or type a quote, adjust the formatting, and click to generate -- pow! You've got an image that's perfectly sized for sharing on Facebook or Twitter. We've found that images like these can really help out an otherwise dull link to a story."

Or something. I didn't edit or re-read that.

[brianboyer]

Also: "Deploys to s3, does not require a server."