enhance_github pages doc (AtsushiSakai#672)

* enhance_github pages doc

* enhance_github pages doc

Author: AtsushiSakai

docs/_templates/layout.html

@@ -0,0 +1,8 @@
+{% extends "!layout.html" %}
+
+{%- block extrahead %}
+{{ super() }}
+<script async
+        src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-9612347954373886"
+        crossOrigin="anonymous"></script>
+{% endblock %}