feat: add google adsense block

Author: qiwihui

_includes/auto-ads.html

@@ -0,0 +1,4 @@
+{% if site.google_adsense %}
+<script data-ad-client="{{ site.google_adsense }}" async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js">
+</script>
+{% endif %}

_layouts/default.html

@@ -12,6 +12,8 @@
         gtag('config', '{{ site.google_analytics }}');
     </script>
     {% endif %}
+
+    {% include auto-ads.html %}
 
     <!-- Non social metatags -->
     <meta charset="utf-8">