docs: add FAQ section

[meichuanyi]

Summary

This PR adds a comprehensive FAQ section to the README.md to help developers quickly understand AIGNE Framework and find answers to common questions.

FAQ Coverage

The FAQ section covers:

• Platform Concept: What is AIGNE Framework and its origin
• Comparison: How AIGNE compares to LangChain and CrewAI
• Quick Start: Installation and basic usage example
• LLM Providers: Supported AI model providers (OpenAI, Anthropic, Gemini, Bedrock, DeepSeek, Ollama, OpenRouter, XAI)
• Workflow Patterns: 8 patterns available (Sequential, Concurrency, Router, Handoff, Reflection, Orchestration, Code Execution, Group Chat)
• AFS: Agentic File System concept and features
• MCP Integration: MCP server/client support and examples
• Local Models: Ollama configuration for local models
• Custom Agents: How to create custom agents
• Error Handling: TypeScript error handling patterns
• Contributing: Contribution guidelines link
• Resources: Documentation, examples, community links

Checklist

• Documentation update only (no code changes)
• FAQ content based on existing README information
• All links verified
• TypeScript-first perspective maintained