In the documentation, make the link to matrix more obvious

Currently on https://profiler.firefox.com/docs/ we have a link at the top right, but it's not obvious that this is a link to a chat for people who don't know about matrix. We should make it more obvious, maybe “💬 Talk to the team on Matrix”
Also possibly add some more contact options to the doc home page itself.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-31)