avoid own chapter for meager pvenode, move to sysadmin

avoid own chapter for meager pvenode, move to sysadmin

As else we have a big promising heading for "PVE Node Management"
with just two acme examples and a bit of Wake-On-LAN support.

Move the latter into sysadmin, the former goes only in man-page
environment, as the ACME docs are much more telling.

Ideally we move some stuff inside pvenode and see if it merits it's
own chapter, separating the more basic "Linux-y" sysadmin stuff from
PVE node, but not today.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>