Update contribution guide
We realized that we have contribution guidelines in the README.md, and also in CONTRIBUTING.md.
Also we should move our internal merge criteria to CONTRIBUTING.md.
Hello! We are running our annual fundraising. Please consider making a donation if you value this freely available service or want to support people around the world working towards liberatory social change - https://riseup.net/donate
We realized that we have contribution guidelines in the README.md, and also in CONTRIBUTING.md.
Also we should move our internal merge criteria to CONTRIBUTING.md.