add meta tag for carpentry type

Author: fmichonneau

_layouts/workshop.html

@@ -20,6 +20,7 @@
     <meta name="instructor" content="{{page.instructor|join:'|'}}" />
     <meta name="helper" content="{{page.helper|join:'|'}}" />
     <meta name="contact" content="{{page.email}}" />
+    <meta name="carpentry" content="{{site.carpentry}}"
     {% if page.redirect %}
     <meta http-equiv="refresh" content="0; url={{page.redirect}}" />
     {% endif %}