minor update to plotly guide

homepage/guide_plotly_interactivity.html

@@ -91,7 +91,7 @@ <h5 style="line-height: 49.2px">8: Toggle Spike Lines</h5>
 
             <h5 style="line-height: 49.2px">9, 10: Show closest data on hover / Compare data on hover</h5>
             <div class="row">
-                This allows you to show the closest data point on hover and compare data points on hover. This is useful for visualizing the data values in a different way. You can do this by hovering over the data points on the plot.
+                This allows you to show the closest data point on hover and compare data points on hover. This is useful for visualizing the data values in a different way. You can do this by hovering over the data points on the plot. The compare feature is useful when you have multiple traces on the plot.
                 <img src="./imgs/screenshots/plotly_demo/img_09_10_labels.gif" alt="Download plot" style="width: 100%; padding: 15px;"/>
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             </div>