nextcloud: add how to disable trusted domains
This PR adds description how to disable trusted domains (related to https://gitlab.labs.nic.cz/turris/turris-os-packages/-/merge_requests/206 )
Self sign-up has been disabled due to increased spam activity. If you want to get access, please send an email to a project owner (preferred) or at gitlab(at)nic(dot)cz. We apologize for the inconvenience.
This PR adds description how to disable trusted domains (related to https://gitlab.labs.nic.cz/turris/turris-os-packages/-/merge_requests/206 )