Update head.html

_includes/head.html

@@ -4,7 +4,12 @@
 	<meta name="viewport" content="width=device-width, initial-scale=1">
 	<meta name="description" content="">
 	<title>{% if page.title %} {{ page.title }} | {% endif %}{{site.title}}</title>
-
+
+	<section class="main-container text">
+		<h2 class="title announcement">This site is out of date.</h2>
+		  To see our most recent course site, <a href="https://harvard-ml-courses.github.io/cs181-web/">click here</a>!
+	</section>
+
 	<!-- CSS files -->
 	<link href="https://fonts.googleapis.com/css?family=Roboto:300,400,500,700&display=swap" rel="stylesheet">
 	<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css"