Add home link.

_includes/page-header.html

@@ -1,5 +1,6 @@
 <section class="page-header">
   <h1 class="project-name">{{ site.title }}</h1>
   <h2 class="project-tagline">{{ site.tagline }}</h2>
+  <a href="http://greenupday.org" class="btn">Home</a>
   <a href="https://github.com/mattbk/greenupday.org" class="btn">View on GitHub</a>
 </section>