Add more analytics

_includes/head/custom.html

@@ -0,0 +1,13 @@
+<!-- start custom head snippets -->
+
+{% if site.gtm %}
+<!-- Google Tag Manager -->
+<script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':
+new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],
+j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src=
+'https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);
+})(window,document,'script','dataLayer','{{ site.gtm }}');</script>
+<!-- End Google Tag Manager -->
+{% endif %}
+
+<!-- end custom head snippets -->