Add demo site

Add a new page for describing and linking to the new demo site.

Signed-off-by: Ben Kochie <superq@gmail.com>

Author: SuperQ

content/demo.html

@@ -0,0 +1,26 @@
+---
+title: Demo
+---
+<div class="row">
+  <div class="col-md-12 doc-content">
+    <h1>Demo</h1>
+    <p>
+      There is a public demo site for Prometheus, Alertmanager, Grafana, and several exporters.
+    </p>
+    <p>
+      <a href="https://demo.do.prometheus.io">View the demo</a>
+    </p>
+    <p>
+      The site is deployed with Ansible and the <a href="https://github.com/cloudalchemy">Cloudalchemy Prometheus roles</a>
+    </p>
+    <p>
+      The source to this demo site is <a href="https://github.com/prometheus/demo-site">prometheus/demo-site</a>
+    </p>
+    <p>
+      Special thanks to <a href="https://digitalocean.com/">DigitalOcean</a> for providing hosting resources.
+    </p>
+    <p>
+      The Prometheus logo was contributed by Robin Greenwood.
+    </p>
+  </div>
+</div>

layouts/header.html

@@ -69,6 +69,7 @@
             <li><a href="/docs/introduction/overview/">Docs</a></li>
             <li><a href="/download/">Download</a></li>
             <li><a href="/community/">Community</a></li>
+            <li><a href="/demo/">Demo</a></li>
             <li><a href="/blog/">Blog</a></li>
             <li><a href="https://github.com/prometheus"><i class="fa fa-github"></i></a></li>
             <li><a href="https://twitter.com/PrometheusIO"><i class="fa fa-twitter"></i></a></li>