The fastest way to get it going would be to add the startup command to
/etc/rc.local/. This is run at the end of the system boot.
The "proper" way is to use the init system. There's a file called
/etc/init.d/skeleton which is a basic framework for making an init script for starting a service. Copy it to /etc/init.d/svnserve and customise it as needed. There's also plenty of examples of svnserve init files on the web. Once
/etc/init.d/svnserver [start|stop] works as expected, you can then run
chkconfig svnserve on. This init script will be then be started on boot, and stopped on shutdown.