docs: the readouts strip hides when empty

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

help/C/org.udpscope.app/overview.page

@@ -117,7 +117,7 @@
         every measurement; <gui>Edit</gui> beside each heading opens that instrument's full
         page. Under them, <gui>Events</gui> lists the captured events, newest first; a click
         replays one and <gui>Manage</gui> opens the full list. While the dock is hidden, or the window is narrow and the
-        dock slides over the plot, the readouts show in a strip under the plot instead.</p>
+        dock slides over the plot, the readouts show in a strip under the plot instead, as long as the cursors are on or there is a measurement.</p>
       </item>
       <item>
         <title>The status bar</title>