Add github link in the docs

Author: alexcanessa

docs/_includes/header.html

@@ -1,5 +1,6 @@
 <div class="site-header">
     <nav class="site-nav">
+        <a class="page-link" href="https://github.com/github-tools/github-release-notes">Github</a>
         {% for page in site.pages %}
             {% if page.title %}
                 <a class="page-link" href="{{ page.url | prepend: site.baseurl }}">{{ page.title }}</a>