Hey, thanks for wanting to contribute to baseimage-docker-centos. :)
If you have a question, please use the Github issue tracker.
If you want to develop baseimage-docker, use the Vagrantfile in the repository. It will setup an Ubuntu VM with Docker installed in it. Use the Makefile to build the Docker image.
All development happens on the next branch. The master branch is supposed to point to the latest stable release, because users read documentation from the master branch.