Stub documents and proposals about our development process

This fleshes out some documentation for docs.zerovm.org. The goal is to make it easy for interested people to see

* How to get started with ZeroVM
* How go contribute
* How to get help

I've also outlined some ideas for how we should do releases and how to organize the branches to support this well. The idea a feature/bugfix of major/minor releases at regular intervals is that is gives users a predictable rhythm and to ensure that we don't leave features and bugfixes unreleased for too long.