Update CONTRIBUTORS.md
Update CONTRIBUTORS.md with installation, build instructions for contributors
Task: #324944
How to register an account on GitLab. To prevent spam, new accounts are locked until approved by an admin or the approver bot. You can also file an unlock request to expedite access.
Support: mw:GitLab, how to host a project on GitLab, #wikimedia-gitlab on libera.chat, #GitLab on Phabricator.
Update CONTRIBUTORS.md with installation, build instructions for contributors
Task: #324944