Adds note to docs that the Preview Window does not execute the rules.

DesignspaceEditor2.roboFontExt/html/index.html

@@ -652,7 +652,7 @@ <h2 id="rules">Rules Tab <a href="#toc">↑</a></h3>
 
 <img alt="screenshot of DSE2 rules tab" src="screenshot_mutatorsans_rulestab.jpg">
 
-<p class="caption">The rules tab is an editor for defining rules and condition sets. Tools may interpret these into <code>rvrn</code> features.</p>
+<p class="caption">The rules tab is an editor for defining rules and condition sets. Tools may interpret these rules into <code>rvrn</code> features. The <a href="#location-preview-window">Preview Window</a> does <b>not</b> show the rules in action. While this would indeed be useful, it requires compiling the features and that is currently outside the scope of this extension. We recommend using <b>FontGoggles</b> for proofing the rules.</p>
 
 <h3>Rules syntax</h3>