Add slack link #11
Description
Add a slack link to the contact page.
I suggest using an open invite for now:
https://join.slack.com/t/openem/shared_invite/zt-2zol5byg0-hQPsS3xb_CPsNk7QsbY8tw
There is also an option to restrict signups to some domains:
https://join.slack.com/t/openem/signup
We could switch to this if we have problems with spam, but it doesn't seem to support wildcard subdomains (eg @id.ethz.ch) so we would have to add a lot of domains to the list.