docs:monitor: Fill in num_nonfunc_rotors_before_error details

The `num_nonfunc_rotors_before_error` attribute contains the number of
fan rotors (sensors) that must be nonfunctional before an error event
log is created. This defaults to 1, meaning that an error event is
logged when any one of the fan rotors (sensors) being monitored is
nonfunctional.

Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
Change-Id: I3294e817c14f1086657861c27c71eb6ad0546f48
1 file changed