Update /cookbooks docs for new params in Supermarket

Supermarket provides two new URL parameters for the `/cookbooks` API endpoint:

* `order` for changing how the results are sorted
* `user` for only showing cookbooks maintained by a specific person

This updates the docs for that endpoint to explain the new parameters.  Here are the relevant commits on the Supermarket project:

https://github.com/opscode/supermarket/commit/c0a787bfb47917bc3a88fb68f0677e8fdad3d632
https://github.com/opscode/supermarket/commit/ad534a4eb30c593fa10eb51cbc1a32278cfead73