create_team_channel: add calendar link to intro message
create_team_channel: add calendar link to intro message

Add a link to the team calendar in the intro message to give it better
visibility. I decided to add it to the intro message rather than the
topic as suggested in the issue as it made the topic a bit messy. This
seemed like the cleaner approach.

Closes #287

cyanfish/heltour,cyanfish/heltour,cyanfish/heltour,cyanfish/heltour