Added ctrl+shift hint in DevTools.

src/Perspex.Diagnostics/DevTools.paml

@@ -8,9 +8,11 @@
     <ContentControl Content="{Binding Content}" Grid.Row="1"/> 
     
     <StackPanel Gap="4" Orientation="Horizontal" Grid.Row="2">
+      <TextBlock>Hold Ctrl+Shift over a control to inspect.</TextBlock>
+      <Separator Width="8"/>
       <TextBlock>Focused:</TextBlock>
       <TextBlock Text="{Binding FocusedControl}"/>
-      <Separator/>
+      <Separator Width="8"/>
       <TextBlock>Pointer Over:</TextBlock>
       <TextBlock Text="{Binding PointerOverElement}"/>
     </StackPanel>