This makes it easier to edit the copy-paste.

Modify documentation to add a new ganeti instance with information about where to add a reverse dns entry in hetzner

The rationale here is we don't want to extend trust from the old
machine, which we do by giving them root access on the new server. By
giving root access to the *old* server, we don't give it access to
anything it already has (or will have, in the case of the ganeti
nodes).

this is starting to look like a thing ansible should be doing

we could have also used the new swap UUID and edited the fstab, but
that would have required more steps:

 1. mount the filesystem
 2. edit fstab
 3. unmount

... and another thing to redo after the last resync.

By enforcing a UUID from the start, we don't need to edit the fstab at
all. I can't think of a compelling reson why reusing the UUID might be
a problem.