examples: Print a description of the program to the console on startup.

examples/template.html

@@ -201,6 +201,7 @@
           if (text) console.error('[post-exception status] ' + text);
         };
       };
+      @print_description@
     </script>
     <script async type="text/javascript" src="@javascript_file@"></script>
   </body>