Linking to source in footer

_includes/footer.html

@@ -3,6 +3,8 @@
   <div class="col-md-12 footertext">
     Copyright &copy; 2016 Software Carpentry Foundation
     /
+    <a href="{{ site.repo }}">Source</a>
+    /
     <a href="{{ site.root }}/license/">License</a>
     /
     <a href="mailto:{{site.email}}">Contact</a>