Clarify PrologSlurmctld configuration parameter use

doc/man/man5/slurm.conf.5

@@ -1169,6 +1169,12 @@ resources for use.
 While this program is running, the nodes associated with the job will be
 have a POWER_UP/CONFIGURING flag set in their state, which can be readily
 viewed.
+The slurmctld daemon will wait indefinitely for this program to complete.
+Once the program completes with an exit code of zero, the nodes will be
+considered ready for use and the program will be started.
+If some node can not be made available for use, the program should drain
+the node (typically using the scontrol command) and terminate with a non\-zero
+exit code.
 A non\-zero exit code will result in the job being requeued (where possible)
 or killed.
 See \fBProlog and Epilog Scripts\fR for more information.