Update example.py with docstring note about letta_client (#2462)

examples/docs/example.py

@@ -8,6 +8,7 @@ If you're using Letta Cloud, replace 'baseURL' with 'token'
 See: https://docs.letta.com/api-reference/overview
 
 Execute this script using `poetry run python3 example.py`
+This will install `letta_client` and other dependencies.
 """
 client = Letta(
     base_url="http://localhost:8283",