added note about aria-value* attrs and status message

Author: fstrr

techniques/aria/technique-using-progressbar-role-with-a-status-message.html

@@ -14,7 +14,10 @@ <h2>Description</h2>
       <section id="example">
 				<h2>Example</h2>
 				<p>This example simulates the progress of uploading a document. The progress of the upload is communicated to the user with an ARIA <code>progressbar</code> and visible text underneath the progress bar. The visible text is contained in an element with an <code>aria-live="polite"</code> attribute. This attribute tells screen readers to announce updates made to the content of the element.</p>
-				<p>The following example can be seen as a <a href="../../working-examples/aria-role-status-progressbar/">working example</a>.</p>
+
+				<p class="note">The <code>aria-valuemin</code>, <code>aria-valuemax</code>, and <code>aria-valuenow</code> values on the <code>progressbar</code> component programmatically communicate the progress of the upload, but because the <code>progressbar</code> role is not a live region screen readers won't announce updates to those values. Programmatically connecting a status message to the <code>progressbar</code> to announce the changes in value, and a final "upload complete" message creates a better user experience.</p>
+
+				<p>The following code can also be seen as a <a href="../../working-examples/aria-role-status-progressbar/">working example</a>.</p>
 
 <pre><code class="language-html">&lt;p id=&quot;upload-progress-label&quot;&gt;Uploading document: &lt;strong&gt;report.pdf&lt;/strong&gt;&lt;/p&gt;
   &lt;div