Document that accessing Mastodon from the host in a UBOS container, by default creates an error

[jernst]

That's because a Mastodon module cannot handle the link-local IPv6 addresses at which the request comes in when the default /etc/nsswitch.conf "mymachines" name resolution is used. Instead, the user needs to add an IPv4 entry to /etc/hosts after https://gitlab.com/ubos/ubos-website/-/issues/7 is done.

[jernst]

This may go away with the new VM configuration. Will see, leaving open for the time being.