Add link to bluebird
Add link to bluebird

[see https://twitter.com/dan_abramov/status/563722315788476416]

Daniel15/promisejs.org,ForbesLindesay/promisejs.org,Daniel15/promisejs.org,ForbesLindesay/promisejs.org,promise-cn/promisejs.org,promise-cn/promisejs.org