This repo needs a CONTRIBUTING.md

[bnoordhuis]

It can probably lift large sections from node's CONTRIBUTING.md.

[orangemocha]

The new template for contributing is also an option: https://github.com/nodejs/TSC/blob/master/BasePolicies/CONTRIBUTING.md

[gibfahn]

This was just added in #771, but it might be worth leaving this open as that doesn't contain anything that's node-gyp specific.