update readme

[tsubakiky]

This pull request significantly enhances the README.md file for the connect-python project, transforming it into a comprehensive guide for users and developers. The updated documentation introduces detailed explanations of the framework's features, installation steps, usage examples, streaming capabilities, multi-protocol support, and development requirements.

Documentation Improvements:

• Framework Overview: Added an introduction to Connect Python, highlighting its interoperability between gRPC and REST, type safety with Protocol Buffers, and compatibility with HTTP infrastructure.
• Quick Start Guide: Included step-by-step instructions for defining services, generating Python code, implementing services, running servers, and using clients.
• Streaming Support: Explained supported streaming patterns (unary, server streaming, client streaming, and bidirectional streaming), including limitations of half-duplex bidirectional streaming.

Developer Resources:

• Installation and Dependencies: Provided installation commands, dependency requirements (including forked libraries), and notes on protocol-specific setups.
• Development Setup: Detailed the requirements for development, recommended tools like uv for package management, and instructions for running tests and conformance checks.

This enhancement makes the README.md file a valuable resource for both new users and contributors, ensuring clarity and ease of use.