Website: slack.grafana.com is dead

### What happened? The Readme contains the following link: > * For general discussions, join us on the [official Slack](https://slack.grafana.com/) team. When trying to open it I get SSL_ERROR_UNRECOGNIZED_NAME_ALERT. ### What did you expect to happen? Website works or is removed from Readme if it was disabled ### Did this work before? don't know ### How do we reproduce it? 1. Open https://slack.grafana.com/ _Removed irrelevant stuff from template_