Add categories to cookbook

source/_includes/site/sidebar.html

@@ -2,6 +2,8 @@
   {% assign url_parts = page.url | split: '/' %}
   {% if url_parts[1] == 'components' %}
     {% include asides/component_navigation.html | compact_newlines %}
+  {% elsif url_parts[1] == 'cookbook' %}
+    {% include asides/cookbook_navigation.html | compact_newlines %}
   {% else %}
     {% include asides/about.html %}