docs: the readouts dock, the cursors and measurement pages

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

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

@@ -25,8 +25,9 @@
         <p>Press the cursors button in the toolbar, or <key>c</key>.</p>
       </item>
       <item>
-        <p>The pane below the plot shows the readings and owns a <gui>Reset</gui> button.
-        Drag a marker to move it.</p>
+        <p>The readings are in the side panel (a read-only copy) and in the cursors panel, which
+        <gui>Edit</gui> beside <gui>Cursors</gui> opens over the plot and which owns a
+        <gui>Reset</gui> button. Drag a marker to move it.</p>
       </item>
       <item>
         <p>The mode dropdown offers four modes: <gui>vertical</gui> (the shared time pair),