tl;dr, you can get $2k/week for up to 10 weeks to work on open source.

There's an application process and you'll get selected by a committee. You have to have a GH profile and you can't work for GitHub or any of their affiliated companies. They are biased toward selecting applicants who:

    Have an active and growing set of users
    Understand how you want to grow and maintain your project
    Wish to pursue open source work full-time