add comment explaining theme-head.html

CrankShaft/templates/page/bones.html

@@ -4,6 +4,7 @@
         <meta charset="utf-8">
         <title>{{ content.html_title }}</title>
         <meta name="description" content="{{ content.meta_description }}">
+        {# Place site wide head code in theme-head.html, it should be included into every template. #}
         {% include "CrankShaft/globals/theme-head.html" %}
         {{ standard_header_includes }}
     </head>