Is there any documentation on setting up channels, etc, in linen? I have set up a community with slack integration - but if I invite people from linen they are unable to post in any of the channels (asks them to join slack..), including the default/general ones that appear to have been created by linen? If I post in a channel, it appears to come from the linen integration bot, so im not sure why they would need to also create accounts there?