This is an alfred workflow. This means you need Alfred. And you need the alfred powerpack.

This workflow makes it easer to search for development documentation across a wide range of languages and frameworks.

To download a pre packaged workflow, check out the main site: http://wemakeawesomesh.it/alfred-dev-doctor

To create your own parsers for documentation searches, check out https://github.com/sydlawrence/alfred-dev-doctor/wiki/Creating-a-Parser

Happy Hacking :)