Add Twitter meta tags

_includes/base/meta.html

@@ -24,6 +24,10 @@
     <meta property="og:image" content="{{ site.logo }}" />
     {% endif %}
 
+    <meta property="og:url" content="{{ page.url | absolute_url }}" />
+
+    <meta name="twitter:card" content="summary" />
+
     <link rel="apple-touch-icon" sizes="180x180" href="{{ site.baseurl }}/images/apple-touch-icon.png">
     <link rel="icon" type="image/png" sizes="32x32" href="{{ site.baseurl }}/images/favicon-32x32.png">
     <link rel="icon" type="image/png" sizes="16x16" href="{{ site.baseurl }}/images/favicon-16x16.png">