javascript: make deprecation notice more prominent

This text is easy to miss as it's only at the top, and in the same size
and weight as other intro text.  If people follow links to sections (as
is the norm for style guides), this will be completely skipped.

Let's make the notice into a sticky butter bar at the top so it's always
shown regardless of where the person is on the page.

javascriptguide.xml

@@ -1,11 +1,12 @@
 <?xml version = '1.0'?>
 <?xml-stylesheet type="text/xsl" href="styleguide.xsl"?>
 <GUIDE title="Google JavaScript Style Guide">
+  <p style="position: fixed; left: 0; top: 0; padding: 0.5em; margin: 0; background-color: #fef6e0; text-align: center; width: 100%; font-weight: bold;">
+    Please note: This guide is old and is not being updated. It is retained
+    as a reference as it was written for pre-ECMAScript 6th Edition features.
+    Please use the a href="jsguide.html">newer guide</a> instead.
+  </p>
   <p class="revision">
-    Please note: there's a newer version of this guide that includes
-    ECMAScript 6th Edition features. It lives <a href="jsguide.html">here</a>.
-    You should probably be using that for new code.
-
     Revision 2.93
   </p>