Add README.md with full repository documentation (Chinese)

[Copilot]

Repository had no documentation explaining its purpose, structure, or usage.

Changes

• Added README.md covering:
  • Project overview: PyTorch study repo spanning AlexNet → VGGNet → ResNet-50 → ViT-B/16, plus multimodal BLIP/CLIP+FAISS
  • Directory structure tree with per-file descriptions
  • Per-module breakdown: architecture details, training config, key features (feature map visualization, Grad-CAM, mixed precision, Warmup+Cosine LR, FAISS index types)
  • BLIP submodule table (PatchEmbedding → BLIPModel) documenting the from-scratch implementation
  • Install commands per module, quick-start run commands, model parameter reference table

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