I've updated the ModeShape Development Workflow article with more detail.
Also, one goal is that all development is done within forks and submitted via pull requests. For the time being, I will be reviewing those pull-requests and merging them into the official repository. But over time, I'd like other contributors to also serve in this capacity (especially to review my changes). As you become comfortable with Git and GitHub, and want to serve as a committer, look at the ModeShape Integration Managers article.
One more link: the ModeShape Development Tools describes the tools that we use in our development environment (like the JDK, Maven, and Eclipse) and provides instructions for installing and configuring Git, creating a GitHub account, and updating your JBoss.org profile so we can associate your Git commits with your JBoss.org profile (and your signed contributor agreement).