docs: the readouts strip hides when empty

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

docs/USER-GUIDE.md

@@ -22,7 +22,7 @@ The window is a plot with three things around it:
 - the **dock** on the right, which the dock button in the header bar (`s`) shows and hides: read-only
   **Readouts** of the cursors and of the measurements, each with an **Edit** button that opens its
   page, and an **Events** block. With the dock hidden, or in a narrow window where the dock slides over the plot, the readouts show in a
-  one-line strip under the plot instead (the cursors' deltas and each measurement's value; **Cursors** and **Measures** open the pages).
+  one-line strip under the plot instead (the cursors' deltas and each measurement's value; **Cursors** and **Measures** open the pages); the strip is there only while the cursors are on or there is a measurement.
 
 ## 1. Connecting