Update ARC getting started doc

chrome/common/extensions/docs/templates/articles/getstarted_arc.html

 <h1>Getting Started with ARC</h1>
 
 <p>
 The App Runtime for Chrome (Beta), or ARC, lets you run your favorite
 Android apps on Chrome OS. By following these steps, you can try out the <a
 href="http://goo.gl/pkt6HV">App Runtime for Chrome (Beta)</a> during this
 Developer Preview.
 </p>
 
 <p>
 To test your app, you need three things:
 <ol>
   <li> Your APK. </li>
-  <li> PC, Mac, Linux, or Chromebook on Chrome Version 41+. </li>
+  <li> PC, Mac, Linux, or Chromebook on Chrome Version 41+.
+  <ul>
+    <li>
+      Note: ARC is no longer supported on 32-bit x86 platforms and those
+      platforms will no longer receive updates after October 13, 2015. All ARM
+      platforms will continue to work and receive updates.
+    </li>
+  </ul>
+  </li>
   <li> <a href="http://goo.gl/gAn0Xh">The ARC Welder app</a>. </li>
 </ol>
 </p>
 
 <h2 id="test">Test your app</h2>
 
 <p>
 Open ARC Welder, attach your APK, and select your options. Click <strong>Launch
 App</strong> to test your app. When testing, <a href="http://goo.gl/megdlG">file
 a bug</a> if something doesn't work, or
@@ skipping 88 matching lines @@
   <li>
     To ensure compatibility with all users, package and test your app on the <a
     href="https://support.google.com/chromebook/answer/1086915?hl=en&source=genius-rts">Chromebook
     Stable channel</a>.
   </li>
   <li>
     To use in-app payments, <a href="arc_in_app_payments.html">read more</a>.
   </li>
 </ul>
 </p>