Hello! I'm flattered that you're considering contributing to the game engine!
I would like the engine to be directed by a few core developers. You can become a core developer by interviewing with me after you have made one (or a few) high quality contributions and demonstrated a solid interest in the engine. The core developers are responsible for approving/denying pull requests and controling the general direction of the game engine/its community.
If you would like to become a contributer, I suggest you start by learning how to use the engine. Then head on over to the documentation and read the developer docs. Play/modify the example projects. Once you have a solid feel for how the engine is organized, its conventions, etc, extend it in some way and send a pull request.
We will be following the github-flow version control pattern, which means that master is always deployable. Branch off master, make your changes, test them, and when you are ready, open a pull request to master. It is worth reiterating, anything that wants to go into master must be tested first.
I look forward to working with you all!