man: add info on status scripts in powerman.dev(5)

Problem: Recent updates altered when an "all" vs "singleton"
status script is called.  However this change is not documented.

Add information on why a user might want to specify both an
"all" and "singleton" status script for power status, beacon status,
and temperature status.

man/powerman.dev.5.in

@@ -81,7 +81,11 @@ Get device in a state so login script will work
 (though hopefully disconnecting will do that too).
 .TP
 .I "status_all, status[%s]"
-Obtain plug state for all plugs or only the specified plug.
+Obtain plug state for all plugs or only the specified plug.  In most
+cases, only one script needs to be specified.  In some hardware where
+unpopulated plugs may be problematic, it may be beneficial to specify
+both.  If both scripts are specified, the status_all script will be
+called only when all plug are requested.
 .TP
 .I "on_all, on_ranged[%s], on[%s]"
 Power on all plugs, a range of plugs, or the specified plug.
@@ -107,11 +111,19 @@ and a probe into the node attached to a non-standby power source.
 Obtain temperature reading for all plugs or only the specified plug.
 Temperature is obtained by sampling a thermocouple in the node.
 Results are reported as a text string - not interpreted by Powerman
-beyond any regex chopping done by the script.
+beyond any regex chopping done by the script.  In most cases, only one
+script needs to be specified.  In some hardware where unpopulated
+plugs may be problematic, it may be beneficial to specify both.  If
+both scripts are specified, the status_all script will be called only
+when all plug are requested.
 .TP
 .I "status_beacon_all, status_beacon[%s]"
-Obtain beacon state for all plugs or only the specified plug.
-Some RPC's include a way to flash a light on a node.
+Obtain beacon state for all plugs or only the specified plug.  Some
+RPC's include a way to flash a light on a node.  In most cases, only
+one script needs to be specified.  In some hardware where unpopulated
+plugs may be problematic, it may be beneficial to specify both.  If
+both scripts are specified, the status_all script will be called only
+when all plugs are requested.
 .TP
 .I "beacon_on[%s]"
 Flash beacon on the specified plug.