docs: write comprehensive README for Visual Search SDK

[Copilot]

The repository had a placeholder README (two lines). This replaces it with a full, scannable reference document.

Changes

• Header — centered title, tagline, and shields.io badges (License, Stars, Issues)
• Overview — SDK purpose with a capability table (image search, video search, fast indexing, easy integration)
• Features — key differentiators: cross-modal search, frame-level video search, pluggable vector backends, built-in encoders (CLIP/ViT/ResNet), batch ingestion, optional REST server mode
• Quick Start — pip install + source install instructions; working Python snippets for image and video index/search flows
• Project Structure — annotated directory tree
• API Reference — table of all VisualSearchClient public methods with signatures and descriptions
• Configuration — Config object example covering model, backend, device, fps, and batch size
• Contributing — fork → branch → PR workflow
• License — Apache 2.0 reference

Original prompt

Make it a beautiful readme.md
for this SDK

Visual Search on video, images,