Give section 3.2 a title

Author: jaredhoberock

exceptions.html

@@ -50,6 +50,7 @@ <h1>Exception reporting behavior</h1>
         </p>
     </cxx-section>
     <cxx-section id="parallel.exceptions.synop">
+      <h1>Header <code>&lt;experimental/exception_list&gt;</code> synopsis</h1>
       <pre>
 namespace std {
 namespace experimental {