Making the public domain real (and international!)

Hi team -

You may be unaware, but there has been **a lot** of conversation going around regarding licensing and contribution agreements. Both on the White House / intergovernmental [Project Open Data](https://github.com/project-open-data/project-open-data.github.io/pull/135) and the [Public Data Platform / Qu](https://github.com/cfpb/qu/pull/94).

Here's the background - public domain, even via governmental work, is vaguely defined domestically. Internationally, it doesn't exist at all, even if the work is produced by the US Government. So both groups on the issues above started looking for the best legally binding mechanism for the public domain. While the Unlicense is elegant, it is *not* written by a lawyer and not vetted. Problems around public domain dedication are more extensively detailed [elsewhere](http://creativecommons.org/about/cc0) so I won't get into the specifics here.

Both groups have come to the consensus that the best legal vehicle to give public domain certainty to developers, whether domestic or international, is the [Creative Commons Zero - Public Domain](http://creativecommons.org/publicdomain/zero/1.0/). Not only is it extensively vetted by lawyers, the CC approach using a human-readable layer supported by a legal code is very successful in giving individuals, non-profits, corporations the legal certainty they need. 

Project Open Data has already made the [change](https://github.com/project-open-data/project-open-data.github.io/blob/master/LICENSE) and [so has Qu](https://github.com/cfpb/qu/blob/master/CONTRIBUTING.md).

This pull request immediately updates the .io site to this effect. Once merged, we should also include `LICENSE` and `CONTRIBUTING` files across the repos. `LICENSE` ensures non-GitHub or local forks maintain that data, while `CONTRIBUTING` [adds a nice hyperlink](https://github.com/blog/1184-contributing-guidelines) to new issues and pull requests.