[Cookbook][WebServer] symfony#5504 add a tip for the --force option on server:start

Author: vincentaubert

Diff for: cookbook/web_server/built_in.rst

@@ -39,6 +39,15 @@ can change the socket passing an IP address and a port as a command-line argumen
 
     $ php app/console server:run 192.168.0.1:8080
 
+.. note::
+
+    You can use the ``--force`` option to force the web server start
+    even if a web server is already running.
+
+    .. code-block:: bash
+
+        $ php app/console server:start --force
+
 .. note::
 
     You can use the ``server:status`` command to check if a web server is