docs: add Simplified Chinese translation (README.zh.md)

[JasonYeYuhe]

Summary

This PR adds a comprehensive Simplified Chinese translation (README.zh.md) for Chroma (AI-native open-source embedding database) to help Chinese-speaking AI engineers and developers understand core concepts, cloud offerings, and API usage.

• Translated overview, Chroma Cloud hosted service description, and installation methods.
• Translated core 4-function Python API code walkthrough (in-memory setup, collection creation, adding documents with automatic embedding/metadata, and vector querying).
• Translated community links, roadmap, contribution guide, and release cadence.
• Added bidirectional language switchers in README.md and README.zh.md.

[claude]

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[github-actions]

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Use an absolute URL for the Chinese README

Because pyproject.toml:7 publishes this root README as the PyPI package description, this relative link is also rendered on pypi.org/project/chromadb/, where it resolves beneath the PyPI project URL rather than to the repository and returns no Chinese README. Use an absolute GitHub URL so the language switch works both on GitHub and on package-index renderings.

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