Update rigctl rigctld man pages to note that dummy device is the default

doc/man1/rigctl.1

@@ -64,7 +64,7 @@ Here is a summary of the supported options:
 .
 .TP
 .BR \-m ", " \-\-model = \fIid\fP
-Select radio model number.
+Select radio model number. Defaults to dummy rig.
 .IP
 See model list (use \(lqrigctl -l\(rq).
 .IP

doc/man1/rigctld.1

@@ -110,7 +110,7 @@ Here is a summary of the supported options:
 .
 .TP
 .BR \-m ", " \-\-model = \fIid\fP
-Select radio model number.
+Select radio model number.  Defaults to dummy device.
 .IP
 See model list (use \(lqrigctl -l\(rq).
 .IP