docs: add Python version requirement note to README (#25)

Clarify that Python 3.10+ is required and highlight support for
both synchronous and asynchronous workflows in the installation section.

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Co-authored-by: Claude <noreply@anthropic.com>

Author: bokelley

README.md

@@ -22,6 +22,8 @@ AdCP operations are **distributed and asynchronous by default**. An agent might:
 pip install adcp
 ```
 
+> **Note**: This client requires Python 3.10 or later and supports both synchronous and asynchronous workflows.
+
 ## Quick Start: Distributed Operations
 
 ```python