Show a link to the docs instead of a button on the untrusted domain page

Before there was a button to "quickly" add the untrusted domain to the config. This button often didn't worked, because the generated URL was often untrusted as well. Thus removing it and providing proper docs seems to be the better approach to handle this rare case.

Also the log should not be spammed by messages for the untrusted domain accesses, because they are user related and not necessarily an administrative issue.

Signed-off-by: Morris Jobke <hey@morrisjobke.de>