Strengten marketing claim on download page (prometheus#1712)

Signed-off-by: Richard Hartmann <richih@richih.org>

Author: RichiH

content/download.html

@@ -13,6 +13,11 @@ <h1>Download</h1>
       </ul>
     </div>
 
+    <p>
+      Download Prometheus, the leading open-source monitoring framework and TSDB.
+      This includes support for PromQL, the powerful Prometheus query language for processing
+      your monitoring data in a flexible way which was not possible before Prometheus and PromQL.
+    </p>
     <p>
       We provide precompiled binaries and <a href="https://hub.docker.com/r/prom/">Docker images</a>
       for most officially maintained Prometheus components. If a component is