nxagent manpage: extend description of keyboard option

nx-X11/programs/Xserver/hw/nxagent/man/nxagent.1

@@ -518,12 +518,15 @@ settings.
 .TP 8
 .I <model>/<layout>
 use the given model and layout. You can not modify keyboard rules,
-variants or options.
-.TP 8
-If \fIkeyboard\fR is omitted the internal defaults of \fBnxagent\fR
-will used (rules: xfree86, layout: us, model: pc102).
+variant or options. Instead preset values are used. These are
+\fIxfree86\fR for rules and empty strings for variant and options.
 .RE
 .TP 8
+
+.PP
+If \fIkeyboard\fR is omitted the internal defaults of \fBnxagent\fR will be used (rules: \fIxfree86\fR, layout: \fIus\fR, model: \fIpc102\fR, empty variant and options).
+
+.TP 8
 .B keyconv=<string>
 set keycode conversion mode