Add missing Demo App reference

When following the guide on Inspecting the Network flow
with Hubble's CLI there are many examples that are based
on the Demo App. This PR adds a note to take users to
the Demo App guide so they can deploy it in case they
would like to run the examples of this guide

Fixes: #15972

Signed-off-by: Lorenzo Fundaró <lorenzofundaro@gmail.com>

Documentation/gettingstarted/hubble_cli.rst

@@ -25,15 +25,10 @@ across the globe, there is almost always someone available to help.
    unsure, run ``cilium status`` and validate that Cilium and Hubble are up and
    running.
 
+.. note::
 
-Generate some network traffic
-=============================
-
-In order to generate some network traffic, run the connectivity test:
-
-.. code-block:: shell-session
-
-   while true; do cilium connectivity test; done 
+    This guide uses examples based on the Demo App. If you would like to run them,
+    deploy the Demo App first. Please refer to :ref:`gs_http` for more details.
 
 Inspecting the cluster's network traffic with Hubble Relay
 ==========================================================