Add header links (#679)

Author: jasongrout

_includes/page-header.html

@@ -7,4 +7,11 @@
     <h1>{{ include.title }}</h1>
   {% endif %}
   <p>{{ include.tagline }}</p>
+
+  <script src="https://cdn.jsdelivr.net/npm/anchor-js/anchor.min.js"></script>
+  <script>
+    document.addEventListener('DOMContentLoaded', function(event) {
+      anchors.add();
+    });
+  </script>
 </header>