docs: Plan for documenting lance-graph on lance.org

I'd like to propose the following plan to document lance-graph in the lance.org official docs site for Lance. I'll discuss with Jack about a potential restructure of how we showcase integrations (like lance-ray and lance-spark), vs. community projects like this one and lance-context.

Key features

• Material theme for mkdocs (same as the rest of the Lance docs).
• A new docs/ directory at the root level of this repo with the mkdocs settings to host the docs within this repo
• A CI job in the main lance repo picks up the static markdown files from this repo and builds the docs for the lance.org on demand
• Every time there is a docs change here, the next time the lance docs are built (at the very least, weekly), the docs update on the main lance.org site

What needs to be documented

SDK reference (autogenerated from code)

• Rust API
• Python API

Quickstart & tutorials

• Create and query a graph in Python + Cypher (using Python library)
• Create and query a graph in Rust + Cypher (using Rust crate)
• Demo Knowledge Graph CLI
• Demo graph visualizer in streamlit

If there's anything missing that would be useful to document, please feel free to add them here. I realize the API is rapidly evolving but I'll work on an AGENTS.md and CLAUDE.md that helps easily keep the docs up to date and move with the velocity of the codebase.