Add nanoseconds units for vcpu.delay doc, as it's based on
'/proc/<pid>/task/<tid>/schedstat' (see 'qemuGetSchedstatDelay()').
'schedstat' is in nanoseconds, according to
https://docs.kernel.org/scheduler/sched-stats.html#proc-pid-schedstat.
Signed-off-by: aadmi <aadmi@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>