:memo: Document process for hacking node module components

@ProbablyCorey documented this process on Discuss and I figured it should be added to the official documentation. I hope that I was able to match the documentation practices the Atom team uses for general documentation.

See: http://discuss.atom.io/t/how-to-setup-development-for-core-modules-like-atom-keymap/9221/18?u=leedohm