docs: add English version to README.md with bilingual navigation

[ZheYanyan]

Summary

This pull request adds an English version of the README to improve accessibility for non-Chinese speakers and support international users and contributors.

Changes

• Added bilingual navigation at the top: [中文](#中文) | [English](#english) for easy language switching
• Added complete English introduction section covering project overview, supported platforms, and core features
• Added quick navigation links to installation and documentation in the English section
• Kept all original Chinese content fully intact, no modifications to existing Chinese documentation
• Pure documentation change, no functional code modifications

Purpose

• Lower the barrier to entry for international users to understand and use the project
• Help expand the user base and attract more global contributors
• Follow open source internationalization best practices

Testing

✅ Verified all anchor links work correctly (Chinese/English navigation jumps to the right sections)
✅ Verified markdown renders properly on both desktop and mobile
✅ File is UTF-8 encoded, no character encoding issues
✅ All external links point to the correct resources
✅ No duplicate content, file remains clean and well-structured

Backwards Compatibility

100% backwards compatible. No changes to existing functionality or Chinese documentation.