Restyled the example demo with bootstrap

* Switched to large input styles to make the demo more appealing
* Added title, description, and link to github repository

## OLD
![stripe_github_io_jquery_payment_example_](https://cloud.githubusercontent.com/assets/740/4030131/6d2c69d2-2c59-11e4-951d-df6c496e82bf.png)

## NEW 
![http___localhost_3000_example__is_not_available](https://cloud.githubusercontent.com/assets/740/4030121/36900654-2c59-11e4-99a4-cedd8b8282ac.png)

Sentence case here, to be consistent.

(i.e., `Restrict numeric`)