Add hook for GA tracking

_config.yml

@@ -31,3 +31,7 @@ aux_links:
 
 # Color scheme currently only supports "dark" or nil (default)
 color_scheme: nil
+
+# Google Analytics Tracking (optional)
+# e.g, UA-1234567-89
+ga_tracking: UA-2709176-10

_includes/head.html

@@ -7,8 +7,21 @@
 
   <title>{{ page.title }} - {{ site.title }}</title>
   <link rel="stylesheet" href="{{ "/assets/css/just-the-docs.css" | absolute_url }}">
+
+  {% if site.ga_tracking != nil %}
+    <!-- Global site tag (gtag.js) - Google Analytics -->
+    <script async src="https://www.googletagmanager.com/gtag/js?id=UA-2709176-10"></script>
+    <script>
+      window.dataLayer = window.dataLayer || [];
+      function gtag(){dataLayer.push(arguments);}
+      gtag('js', new Date());
+
+      gtag('config', '{{ site.ga_tracking }}');
+    </script>
+  {% endif %}
+
   {% if site.search_enabled != nil %}
-  <script type="text/javascript" src="{{ "/assets/js/vendor/lunr.min.js" | absolute_url }}"></script>
+    <script type="text/javascript" src="{{ "/assets/js/vendor/lunr.min.js" | absolute_url }}"></script>
   {% endif %}
   <script type="text/javascript" src="{{ "/assets/js/just-the-docs.js" | absolute_url }}"></script>