[refactor] update docs

[SauravMaheshkar]

📌 Checklist before creating the PR

• [x] The title follows the standard format: [doc/gemini/tensor/...]: A concise description

📝 What does this PR do?

This PR aims to move the README-zh-Hans.md and REFERENCE.md into the docs/ directory and update the paths in the README to clean up the project structure without any functional change.

💥 Checklist before requesting a review

• [x] My PR clearly describes the problem/feature/proposal, with diagrams/charts/table/code if possible
• [x] I have performed a self-review of my code

⭐️ Do you enjoy contributing to Colossal-AI?

• [x] 🌝 Yes, I do ❤️ ❤️ ❤️