doc: update the python repo's readme (#67)

Author: ChunxuTang

python/README.md

@@ -1,10 +1,152 @@
-# Lance Graph Python Package
+# Lance Graph
 
-This package exposes the Cypher graph query interface that wraps the
-`lance-graph` Rust crate. Development uses [uv](https://docs.astral.sh/uv/)
-to manage dependencies inside a project-local `.venv`.
+**A high-performance Cypher-capable graph query engine with Python bindings for building scalable, serverless knowledge graphs.**
 
-## Quick start
+Lance Graph combines a Rust-powered Cypher query engine with Python APIs for:
+- Fast graph queries using Cypher query language
+- AI-powered knowledge extraction from text (via LLM)
+- Lance-backed storage for efficient graph data management
+- Natural language Q&A over your knowledge graphs
+- FastAPI web service for graph queries
+
+## Installation
+
+```bash
+pip install lance-graph
+```
+
+## Quick Start
+
+### 1. Simple Cypher Query
+
+```python
+import pyarrow as pa
+from lance_graph import CypherQuery, GraphConfig
+
+# Create sample data
+people = pa.table({
+    "person_id": [1, 2, 3, 4],
+    "name": ["Alice", "Bob", "Carol", "David"],
+    "age": [28, 34, 29, 42],
+})
+
+# Configure graph schema
+config = (
+    GraphConfig.builder()
+    .with_node_label("Person", "person_id")
+    .build()
+)
+
+# Execute Cypher query
+query = CypherQuery("MATCH (p:Person) WHERE p.age > 30 RETURN p.name, p.age")
+result = query.with_config(config).execute({"Person": people})
+
+print(result.to_pydict())
+# Output: {'name': ['Bob', 'David'], 'age': [34, 42]}
+```
+
+### 2. Build a Knowledge Graph from Text
+
+```python
+from pathlib import Path
+from knowledge_graph import (
+    KnowledgeGraphConfig,
+    LanceKnowledgeGraph,
+    LanceGraphStore,
+    get_extractor,
+)
+from knowledge_graph.cli.ingest import extract_and_add
+
+# Initialize knowledge graph
+config = KnowledgeGraphConfig.from_root(Path("./my_graph"))
+config.ensure_directories()
+
+# Create schema
+schema_path = config.resolved_schema_path()
+if not schema_path.exists():
+    schema_content = """
+nodes:
+  Entity:
+    id_field: entity_id
+
+relationships:
+  RELATIONSHIP:
+    source: source_entity_id
+    target: target_entity_id
+"""
+    schema_path.write_text(schema_content, encoding="utf-8")
+
+store = LanceGraphStore(config)
+store.ensure_layout()
+
+graph_config = config.load_graph_config()
+kg = LanceKnowledgeGraph(graph_config, storage=store)
+kg.ensure_initialized()
+
+# Extract and add entities/relationships from text
+# Using heuristic extractor for testing without API key
+extractor = get_extractor("heuristic")
+# or using LLM extractor (requires API key)
+# extractor = get_extractor("llm", llm_model="gpt-4o-mini")
+text = """
+Albert Einstein developed the theory of relativity at Princeton.
+Marie Curie discovered radioactivity in Paris.
+"""
+
+extract_and_add(text, kg, extractor, embedding_generator=None)
+
+# Query the graph
+result = kg.query("""
+    MATCH (e:Entity)
+    RETURN e.name, e.entity_type
+    LIMIT 10
+""")
+print(result.to_pylist())
+```
+
+### 3. Natural Language Q&A
+
+```python
+from knowledge_graph.llm.qa import ask_question
+
+# Ask questions in natural language
+answer = ask_question(
+    "Who discovered radioactivity?",
+    kg,
+    llm_model="gpt-4o-mini"
+)
+print(answer)
+# Output: Marie Curie discovered radioactivity.
+```
+
+## Command-Line Interface
+
+Lance Graph includes a CLI for building and querying knowledge graphs:
+
+```bash
+# Initialize and extract
+knowledge_graph --root ./my_graph --init
+knowledge_graph --root ./my_graph --extract-and-add notes.txt
+
+# Query with Cypher
+knowledge_graph --root ./my_graph "MATCH (e:Entity) RETURN e.name LIMIT 10"
+
+# Natural language Q&A
+knowledge_graph --root ./my_graph --ask "Who discovered DNA?"
+```
+
+For complete CLI documentation and examples, see the [main README](../README.md#cli-usage).
+
+## Requirements
+
+- Python 3.11+
+- Optional: OpenAI API key for LLM extraction
+
+## Contributing
+
+Lance Graph is open source! Contributions are welcome.
+
+### Quick start
 
 ```bash
 cd python
@@ -16,7 +158,7 @@ maturin develop
 pytest python/tests/ -v
 ```
 
-## Development workflow
+### Development workflow
 
 For linting and type checks:
 
@@ -46,11 +188,15 @@ maturin develop
 - `python/python/knowledge_graph/` – CLI, FastAPI, and extractor utilities built on Lance
 - `python/python/tests/` – graph-centric functional tests
 
-Refer to the repository root `README.md` for information about the Rust crate.
+For more information on development setup, building from source, running tests, and code quality guidelines, see [DEVELOPMENT.md](./DEVELOPMENT.md).
+
+## License
+
+Apache 2.0
+
+## Links
 
-> Run CLI commands through `uv run knowledge_graph ...`. The default uses an
-> LLM-backed extractor; install the LLM extra with `uv sync --extra llm` (or
-> `uv pip install -e '.[llm]'`) and configure `OPENAI_API_KEY`. Install
-> `uv sync --extra lance-storage` to enable Lance dataset persistence. Supply
-> extra options (e.g., `base_url`, HTTP headers) via `--llm-config`. Use
-> `--extractor heuristic` to avoid LLM calls during testing or offline work.
+- [GitHub](https://github.com/lancedb/lance-graph)
+- [Documentation](https://deepwiki.com/lancedb/lance-graph)
+- [PyPI](https://pypi.org/project/lance-graph/)
+- [LanceDB](https://lancedb.com/)