Update contribution guide
Our GitLab instance has now been opened to the public. Everybody is allowed to create an account immediately. However, people who are not members of our research group will receive an External User account only. The contribution guide in
CONTRIBUTING.md should reflect that.
Update the "GitLab Account" section of the contribution guide and invite possible contributors to create an account and join the DORiE project.
How to test the implementation?
Nothing to test.