Update readme async docs

[LifeJiggy]

📝 Update README: AsyncClient Documentation & Usage Examples

This PR enhances the project’s README by adding comprehensive documentation and clear usage examples for the newly exposed AsyncClient functionality.

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✨ Changes Made

• Installation Instructions:
  • Added guidance for installing with async support:

    pip install pydo[aio]

• Quickstart Section:
  • Introduced a new AsyncClient usage example alongside the existing synchronous Client example.
  • Clarified import statements for both:
    • Synchronous: from pydo import Client
    • Asynchronous: from pydo import AsyncClient

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💡 Impact

• Better Documentation:
  Users now have straightforward guidance for leveraging async operations in their projects.
• Improved Discoverability:
  AsyncClient is now prominently featured in the main documentation.
• Complete Examples:
  Both synchronous and asynchronous usage patterns are clearly demonstrated, making it easier for users to adopt either approach.

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🗂️ Files Changed

• README.md — Expanded installation and usage documentation.

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🔄 Backward Compatibility

• All existing documentation remains unchanged.
• No breaking changes to existing functionality or interface.

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Feedback and suggestions are welcome!