Missing sign-in button for Slack footer call-out

[buddyp450]

slack.codeforgreensboro.org is using an outdated version of https://github.com/rauchg/slackin that has a missing sign-in button.

Separate issue, I can't submit a pull request to update the version because it's not version controlled in this project. 😞

[sommanita]

Thanks - we'll jump on this in the morning!