Link to Slack invite is dead

[Fil]

https://github.com/bcoe/c8/blob/main/CONTRIBUTING.md has a link to get an invite for the node-tooling/c8 channel, but the link is dead.

(I wanted to ask a generic question, as a user, and I'm not sure where to do it; if the Slack is closed, would you want to activate the "discussions" tab in this repo?)

thanks.