add google analytics to template

Author: aeftimia

docs/_templates/layout.html

@@ -0,0 +1,13 @@
+{% extends "!layout.html" %}
+
+{% block extrahead %}
+{{ super() }}
+<script async src="https://www.googletagmanager.com/gtag/js?id=G-2BGSHYDJP8"></script>
+<script>
+  window.dataLayer = window.dataLayer || [];
+  function gtag(){dataLayer.push(arguments);}
+  gtag('js', new Date());
+
+  gtag('config', 'G-2BGSHYDJP8');
+</script>
+{% endblock %}