For the netatalk 2.2 version that's still part of Raspbian (why-oh-why is every Linux distro so out of date on so much stuff??) I had to use the following:
# add line at end of file
service netatalk restart
This looks funny, but basically says "configure a server named Your Machine with the default options".
Note that the netatalk daemon is primarily an AFP server. Your machine may also use the Avahi daemon to advertise itself over mDNS, in which case you may also want to change the host name there:
sudo vi /etc/avahi/avahi-daemon.conf
service avahi-daemon restart