github docs say that:

> Invitations are sent via email and can be accepted at https://github.com/azimuth-project

and

> If the user is not a member of your organization, they'll receive an email inviting them to the organization. They will need to accept the invitation before becoming a member of the organization.

Did you get an email invite? I don't know what that would have told you to do. I still can't remember what I had to do before :(.