As of May 2019, this is currently the way to become a Zope contributor; there will likely soon be an updated and less clunky-worded Contributor License Agreement but for now this is the procedure:
Applying for Committer Status
Detailed instructions for gaining commit rights to the Zope repositories are at https://plone.org/foundation/contributors-agreement/contributors-agreement-explained.
- Print, fill out and sign the Plone Contributor Agreement. On page 2 enter Zope in the field for program.
- Scan the agreement (a clear picture/PDF from a phone will suffice, if it's readable enough) and submit it by email to firstname.lastname@example.org
- You will be added to the GitHub repository shortly.