Fix looks, update screenshot, update README information

README.adoc

@@ -10,7 +10,8 @@ Run `sensei-raw-ctl --help` or `man sensei-raw-ctl` for usage information.
 
 If you don't fancy command line tools, there's also a basic GTK+ frontend
 available.  On Ubuntu and its derivatives, you should be able to find it in your
-System Settings.
+System Settings, though this feature has disappeared completely with newer GNOME
+versions.
 
 image::sensei-raw-ctl-gui.png[align="center"]
 

sensei-raw-ctl-gui.ui

@@ -31,6 +31,7 @@
   <property name='border-width'>10</property>
   <child><object class='GtkNotebook' id='notebook'>
    <property name='show-tabs'>FALSE</property>
+   <property name='show-border'>FALSE</property>
    <child><object class='GtkHBox' id='probing_box'>
     <property name='halign'>GTK_ALIGN_CENTER</property>
     <property name='valign'>GTK_ALIGN_CENTER</property>