message: Doc: Clarify use of canonicalize_javascript_libraries with defer_javascript in doc
diff: @@ -215,6 +215,11 @@ The canonical library is <em>not</em> combined with the other two JavaScript
  files, since this would lose the bandwidth and caching benefits of fetching it
  from the canonical URL.
  </p>
  +<p>
  +If <a href="filter-js-defer">defer_javascript</a> is enabled, <em>and</em> library
  +is <em>not</em> tagged with <code>data-pagespeed-no-defer</code>,
  +the canonicalized library is deferred.
  +</p>
  <h2>Requirements</h2>
  <p>
  