Add ID.

Author: Florian Kissling

docs/options.html

@@ -19,7 +19,7 @@ <h1>
 <div class="row">
   <div class="col-md-9" role="main">
     <section id="core">
-      <h1 class="page-header">Core options</h1>
+      <h1 id="core-options" class="page-header">Core options</h1>
 
       <p>
         Select2 supports a small subset of options in every build that is