Add FAQ section to React Native macOS documentation

[Copilot]

This PR adds a comprehensive FAQ section to the React Native macOS documentation, addressing three key questions that developers commonly ask:

Added FAQ Topics

1. What is an out of tree platform?

• Explains the concept of out-of-tree platforms in React Native
• Details how React Native macOS fits into this model
• Lists key characteristics like separate repositories, independent versioning, and platform-specific features

2. What about Mac Catalyst?

• Compares Mac Catalyst vs React Native macOS approaches
• Highlights the advantages of React Native macOS for native macOS experiences
• Explains why React Native macOS is recommended for the best macOS user experience

3. Does Expo support React Native macOS?

• Clarifies current Expo support limitations for macOS
• Provides alternative approaches for developers wanting both Expo and macOS support
• Discusses future possibilities and current workarounds

Implementation Details

• Created docs/FAQ.md with proper markdown formatting
• Structured content with clear headings and bullet points
• Provided actionable information and practical guidance
• Maintained consistent tone and style throughout

The FAQ section provides developers with clear, comprehensive answers to help them make informed decisions about using React Native macOS in their projects.

Fixes #14.

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