Document new pinger hooks.

www/swreg/swreg.inc.php

@@ -222,6 +222,12 @@ $MDF_OVERRIDES = array(
 //   ARGS: <HOOK_NAME> <REMOTE_IP> <SERIAL_NO> <PID>
 //  ERROR: Called when a new request cannot be serviced due to an error
 //   ARGS: <HOOK_NAME> <REMOTE_IP> <SERIAL_NO> <PID> <MSG>
+
+// PINGER (hooks called when a device becomes reachable or unreachable)
+//  REACHABLE  : Called when a device transitions to a reachable state
+//    ARGS: <HOOK_NAME> <SERIAL_NO> <DEVICE_IP>
+//  UNREACHABLE: Called when a device transitions to an unreachable state
+//    ARGS: <HOOK_NAME> <SERIAL_NO> <DEVICE_IP>
 // OPTIONAL
 $HOOKS = array(
     'VERIFY' => array(