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

[JasonYeYuhe]

Description

This PR introduces a comprehensive, high-quality Simplified Chinese translation (README.zh.md) for MLX Examples to help Chinese-speaking developers, researchers, and Apple Silicon machine learning practitioners explore and build with MLX.

Key Changes

• 1:1 Full Translation (README.zh.md):
  • Full catalog of standalone MLX examples across Text, Image, Video, Audio, Multimodal, and Other domains.
  • Links to key models: LLaMA, Mistral, Mixtral 8x7B (MoE), LoRA/QLoRA, T5, BERT, FLUX, Stable Diffusion/SDXL, Wan2.1, Whisper, EnCodec, MusicGen, CLIP, LLaVA, SAM, GCN, and Real NVP.
  • Hugging Face MLX Community model hub integration and citation instructions.
• Bidirectional Navigation: Added language switchers (English · 简体中文) at the top of both README.md and README.zh.md.
• Community Maintenance Notice: Attached volunteer maintenance note (@JasonYeYuhe).

Checklist

• Commits are signed off with DCO (git commit -s).
• All relative and absolute links verified for 1:1 parity and integrity.
• No changes made to Python scripts, notebooks, or dependencies.