enhance_github pages doc (AtsushiSakai#676)

Author: AtsushiSakai

docs/_templates/layout.html

@@ -1,13 +1,6 @@
 {% 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 %}
-
-{% block content %}
+{% block sidebartitle %}
 {{ super() }}
 <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-9612347954373886"
      crossorigin="anonymous"></script>