docs: source badge name only, no signals lock, the Add-a-signal page

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

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

@@ -127,7 +127,7 @@
         and port.</p>
       </item>
       <item>
-        <p><em>Enable a signal</em> in the signal list. The plot stays empty for the first
+        <p><em>Enable a signal</em> in the <gui>Add a signal</gui> page (the <gui>+</gui> badge). The plot stays empty for the first
         fraction of a second while the first window fills — the buffer holds only what has
         arrived.</p>
       </item>