Update 3-setting_workbench_preferences.adoc

org.eclipse.titan.designer/docs/Eclipse_Designer_userguide/3-setting_workbench_preferences.adoc

@@ -156,6 +156,9 @@ image::images/3_hover_window_content.png[title="Hover window content"]
 
 [[debug]]
 == Debug
+
+_Please note that this option is only available if you enable "Display debug preferences" under "TITAN Preferences" (see <<TITAN Preferences, here>>)._
+
 [[debug-options]]
 image::images/3_F12.png[title="Debug options and Load Balancing"]