Slack invite link is broken in the README

[redeux]

Describe the bug
The Slack invite link is broken in the README. It just redirects to the main page for the signup service.

Expected behavior
A signup page for the Haraka slack server

Observed behavior
Main page redirect

Steps To Reproduce
Click the Join us on Slack link in the README

[msimerson]

I just fired up Slack for the first time in ... um, a while. I scrolled through our channel and 95% of the posts are automated posts from GitHub, every time an issue or PR is created or updated. Issue #2996 makes me think that joining slack is already an issue and likely will remain so. In light of that, should we just change the link to GitHub Discussions?

[superman20]

I'd be in favor of just using GitHub Discussions. I like the format and usability better than Slack and I also like having all Haraka info in just 1 place.

[nogginbox]

I just found this discussion.

I had already added a github issue about the slack group invite not working on the community page. Discussions seems like a better place than Slack for this sort of stuff.