Link to useful Prometheus support page (#1938)

Signed-off-by: Richard Hartmann <[email protected]>

Author: RichiH

content/support-training.html

@@ -66,7 +66,7 @@ <h2>Commercial support</h2>
           </div>
 
           <div class="col-md-3 col-sm-6 doc-content tc-col">
-              <a href="https://grafana.com/" class="btn btn-training btn-default btn-large" target="_blank">
+              <a href="https://grafana.com/oss/prometheus/" class="btn btn-training btn-default btn-large" target="_blank">
                 <img src="../assets/commercial-support-logos/grafana-labs.svg" alt="Grafana Labs">
               </a>
           </div>