join slack workspace / channel

I don't know how to join the slack channel or workspace. I use the slack desktop app and i dont see how to add another workspace.

In the browser version it asks me for an E-Mailadress that contains @association.drupal.org. I dont have this. It says if i don't have this type of mailadress, i should have an invitation of the group admin. But there is no contact or way shown how to ask for the invitation. Maybe i dont see something: https://drupal.slack.com/signup?redir=%2Farchives%2FC01ATJ3230E#/domain-...

Would be happy somebody can explain.