docs: Change the Python version to 3.11 (#558)

# Description

Match the actual version information in
[pyproject.toml](https://github.com/google/A2A/blob/main/samples/python/pyproject.toml).

---------

Co-authored-by: Andy <[email protected]>

Author: Linux2010

samples/python/README.md

@@ -15,7 +15,7 @@ Host applications that use the A2AClient. Includes a CLI which shows simple task
 
 ## Prerequisites
 
-- Python 3.13 or higher
+- Python 3.11 or higher
 - [UV](https://docs.astral.sh/uv/)
 
 ## Running the Samples

samples/python/agents/README.md

@@ -6,6 +6,8 @@ Each agent can be run as its own A2A server with the instructions on its README.
 
 To interact with the servers, use an A2AClient in a host app (such as the CLI). See [Host Apps](/samples/python/hosts/README.md) for details.
 
+## Agents Directory
+
 * [**Google ADK**](/samples/python/agents/google_adk/README.md)  
 Sample agent to (mock) fill out expense reports. Showcases multi-turn interactions and returning/replying to webforms through A2A.