docs: Added comment about a known limitation of AgentEventLogger (#2930)

# What does this PR do?
`AgentEventLogger` only supports streaming responses, so I suggest
adding a comment near the bottom of `demo_script.py` letting the user
know this, e.g., if they change the `stream` value to `False` in the
call to `create_turn`, they need to comment out the logging lines.

See https://github.com/llamastack/llama-stack-client-python/issues/15 

<!-- If resolving an issue, uncomment and update the line below -->
<!-- Closes #[issue-number] -->

## Test Plan
<!-- Describe the tests you ran to verify your changes with result
summaries. *Provide clear instructions so the plan can be easily
re-executed.* -->

---------

Signed-off-by: Dean Wampler <dean.wampler@ibm.com>

docs/source/getting_started/demo_script.py

@@ -52,11 +52,16 @@ agent = Agent(
 prompt = "How do you do great work?"
 print("prompt>", prompt)
 
+use_stream = True
 response = agent.create_turn(
     messages=[{"role": "user", "content": prompt}],
     session_id=agent.create_session("rag_session"),
-    stream=True,
+    stream=use_stream,
 )
 
-for log in AgentEventLogger().log(response):
-    log.print()
+# Only call `AgentEventLogger().log(response)` for streaming responses.
+if use_stream:
+    for log in AgentEventLogger().log(response):
+        log.print()
+else:
+    print(response)