doc: add more description on libvirtd option timeout

daemon/libvirtd.pod.in

@@ -54,7 +54,10 @@ Use this name for the PID file, overriding the default value.
 
 =item B<-t, --timeout> I<SECONDS>
 
-Exit after timeout period (in seconds) expires.
+Exit after timeout period (in seconds) elapse with no client connections
+or registered resources.  Be aware that resources such as autostart
+networks will result in never reaching the timeout, even when there are
+no client connections.
 
 =item B<-v, --verbose>