Adds og:image to header.

Author: tebjan

custom template/vvvv/partials/head.tmpl.partial

@@ -15,6 +15,7 @@
   <link rel="stylesheet" href="{{_rel}}styles/site.css">
   <meta property="docfx:navrel" content="{{_navRel}}">
   <meta property="docfx:tocrel" content="{{_tocRel}}">
+  <meta property="og:image" content="images/vvvv_og.png">
   {{#_noindex}}<meta name="searchOption" content="noindex">{{/_noindex}}
   {{#_enableSearch}}<meta property="docfx:rel" content="{{_rel}}">{{/_enableSearch}}
   {{#_enableNewTab}}<meta property="docfx:newtab" content="true">{{/_enableNewTab}}