add link-tag for rss feed

_includes/head.html

@@ -9,6 +9,8 @@
 	<link rel="stylesheet" href="{{ "/css/main.css" | prepend: site.baseurl }}">
 	<link rel="canonical" href="{{ page.url | replace:'index.html','' | prepend: site.baseurl | prepend: site.url }}">
 
+	<link rel="alternate" type="application/rss+xml" title="RSS" href="/feed.xml">
+
 	<link href="/css/font-awesome.min.css" rel="stylesheet">
 	<script src="/js/jquery.min.js"></script>
 </head>