docs: Add FAQ section for common questions

[meichuanyi]

Fixes N/A

This PR adds a comprehensive FAQ section to the README, addressing common questions about:

• Project overview and positioning
• Comparison with other frameworks
• Key features and benefits
• Getting started instructions
• LLM/provider support
• Documentation and help resources
• License information

✅ Documentation only change
✅ No code modifications

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Latest commit: 32232fb

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