Slack workspace for questions, issues and discussion

I setup a free Slack workspace called TileMill, to aid in discussion of issues, etc. I think I set it up correctly, but not sure if people can request to join, or if I have to invite them individually? I've never setup Slack for open source type project, only enterprise.

Slack workspace is tilemill.slack.com.

Open to suggestions or instructions on how to properly setup the Slack workspace for TileMill.