[Tracking][WebLLM] Revamp documentations

[CharlieFRuan]

We'd like to complete the following items for WebLLM documentation

• [ ] Update github README: https://github.com/mlc-ai/web-llm
  • Also make sure npm package is sync'd https://www.npmjs.com/package/@mlc-ai/web-llm
• [ ] Update / re-organize website: https://webllm.mlc.ai/
  • [ ] e.g. Add code snippet to show case simple usage
• [ ] Re-organize documentation: https://llm.mlc.ai/docs/deploy/javascript.html
  • WebLLM Quickstart (brief intro to the project, quick start example)
  • OpenAI-like Capabilities
    • Chat completion
    • Streaming
    • JSON mode & JSON schema
    • Function calling
    • Logit processing
    • Seeding
  • Supported Models
    • Prebuilt Models
    • Verify Installation for compiling models
    • Bring Your own model variant
    • Bring your own model library
  • Building agents / WebApp with WebLLM
    • Service Worker
    • Web Worker
    • Chrome extension
  • FAQ & API (a link to typedoc)