How to contribute?

I would have benefited from a `hacking.md` or **Contributing** section added to the README.

After grokking how `generator-donejs` ties into both `donejs/cli` and `donejs/donejs`, I was able finally to deduce the following steps, and see the result of my edits in `generator-donejs/plugin`:
1. Clone `donejs/generator-donejs`.
2. Run `npm link` within the cloned directory.
3. Make a new temporary directory for testing.
4. Run `npm link generator-donejs` within that new testing directory.
5. Finally, `donejs add plugin` will use the linked generator, because it already exists there.

If there is a better way of setting up this project to hack on it and test generator changes, I'd like to know.

Assuming documentation does not already exist regarding how to set this up, an explanation of these steps would be very helpful for new contributors like me! Thanks 👍