Fix: typo

docker/docker_log_centralizer/index.html

@@ -253,7 +253,7 @@
 <li><a href="https://github.com/Febbweiss/docker-java-log-generator">Java log generator</a> - A container generating Java logs (with exception stack trace)</li>
 </ul>
 <h2 id="how-it-works">How it works</h2>
-<p>There are 2 agent types :</p>
+<p>There are 3 agent types :</p>
 <ul>
 <li>Filebeat</li>
 <li>Logstash-Forward</li>