Dynamically generate a heading for Extension Docs API pages

chrome/common/extensions/docs/templates/intros/declarativeWebRequest.html

-<h2 id="notes">Notes</h2>
-
-<p>
-Use the <code>chrome.declarativeWebRequest</code> module to intercept, block, or
-modify requests in-flight. It is significantly faster than the <a
-  href="webRequest.html"><code>chrome.webRequest</code> API</a> because you can
-register rules that are evaluated in the browser rather than the
-JavaScript engine which reduces roundtrip latencies and allows very high
-efficiency.
-</p>
-
 <h2 id="manifest">Manifest</h2>
 
 <p>
 You must declare the "declarativeWebRequest" permission in the
 <a href="manifest.html">extension manifest</a> to use this API,
 along with <a href="declare_permissions.html">host permissions</a>.
 </p>
 
 <pre>{
   "name": "My extension",
@@ skipping 229 matching lines @@
 chrome.declarativeWebRequest.onRequest.addRules([rule1, rule2]);
 </pre>
 
 <p>
 It is important to recognize that the <code>IgnoreRules</code> action is not
 persisted across <a href="#evaluation">request stages</a>. All conditions of
 all rules are evaluated at each stage of a web request. If an
 <code>IgnoreRules</code> action is executed, it applies only to other actions
 that are executed for the same web request in the same stage.
 </p>