Add Slack workspace link to Org readme

[jeremyeder]

Right around the 17th, please add a reference to the instructlab slack workspace so folks can generate invites for themselves. https://join.slack.com/t/instruct-lab

[lhawthorn]

So, the way we handle this is we have an invite link that expires every 30 days. Rather than have to update that link in all the places every 30 days, I propose we have prominent linking to the Project FAQ, which will not only orient folks to the project but also send them to the InstructLab Slack Guide which can serve as our SSOT and only update one place for the Slack invitation link.

If you are cool with this approach @jeremyeder please close this issue.

[lhawthorn]

I believe this issue has been resolved satisfactorily. If you disagree, please reopen it.