Improve README files with latest code information and fix inconsistencies

[Copilot]

This PR addresses several issues in the README files to bring them up to date with the latest codebase and fix various inconsistencies:

Key Improvements

Added Doge2 Architecture Information

• Introduced comprehensive documentation for the new Doge2 enhanced architecture
• Added details about improved Mixture of Experts design with up to 900 experts and 15 experts per token
• Documented better scalability and extended vocabulary support (up to 49,152 tokens)
• Added news entry announcing Doge2 introduction

Fixed Content Issues

• Fixed typo: Corrected "Doge-320" to "Doge-320M" in news section for consistency
• Fixed alt text: Changed "samlldoges" to "smalldoges" in main logo image
• Standardized links: Made dataset link formatting consistent across all tables
• Updated Quick Start: Added references to both Doge and Doge2 training materials

Enhanced Documentation Structure

• Added comprehensive Doge2 section with technical specifications
• Updated architecture description to cover both Doge and Doge2 variants
• Improved navigation with proper links to training guides and notebooks
• Added Chinese notebook reference for better accessibility

Ensured Consistency

• Synchronized both English and Chinese README versions
• Verified all internal links point to existing files
• Maintained consistent formatting throughout both documents

Files Changed

• README.md - English version with all improvements
• README_zh.md - Chinese version with corresponding updates

The README files now accurately reflect the current state of the codebase, including the new Doge2 architecture, and provide better guidance for users getting started with the project.

Fixes #137.

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