I don’t know for sure about beta11, but you can certainly do this in beta12.
Click on the DNS link on the left. Then click on new “SOA” to create the new domain, then add your entries there.
When doing this you want to use a domain that is not going to conflict with anything. Windows typically does “domain.local” but I think that even Microsoft is now saying that is not a good idea. Probably because Zeroconf and other automatic name assignment protocols use “.local”.
The other widely use recommendation is to take your public domain, say “company.com” and add on something you will never use on the Internet for the base of your naming. Say “hq.company.com”. Then start your naming there. “zeroshell.hq.company.com”, “server.hq.company.com”, etc.