docs: reorganize docs, align homepage copy, and fix build deps (#167)

## Summary

Reorganize the documentation into a Markdown-based structure, update the
docs homepage content, and keep the README aligned with the new
documentation entry points.

## Solution Description

Split the legacy README content into guide pages, move installation into
the docs homepage, remove deprecated sections (RAG demo and license)
from the guide, add contributing info, and normalize guide heading
levels. Added `sphinx-multiversion` to dev dependencies to ensure docs
build cleanly.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Documentation**
* Added comprehensive user guides covering client connection, collection
management, data operations, and embedding functions
  * Added AdminClient documentation with database management examples
* Added RAG demo guide with three embedding modes (default, local, API)
* Reorganized README to highlight documentation link and quick-start
examples
  * Added contributor development and testing guide

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: wangyunlai <hnwyllmm@126.com>

Author: PsiACE

CONTRIBUTING.md

@@ -0,0 +1,78 @@
+# Contributing
+
+Thanks for your interest in contributing to pyseekdb. This file covers development and testing
+instructions.
+
+## Development
+
+- Use Python 3.11+.
+- This repo uses `uv`. You can override the binary via `UV=...`.
+
+This project uses [uv](https://docs.astral.sh/uv/) as the package manager with
+[pdm-backend](https://pdm-backend.fming.dev/) as the build backend. All common development
+tasks are unified through the `Makefile`.
+
+### Prerequisites
+
+Install uv:
+
+```bash
+# macOS/Linux
+curl -LsSf https://astral.sh/uv/install.sh | sh
+
+# Windows
+powershell -ExecutionPolicy ByPass -c "irm https://astral.sh/uv/install.ps1 | iex"
+
+# Or via pip
+pip install uv
+```
+
+### Setup Development Environment
+
+```bash
+# Clone the repository
+git clone https://github.com/oceanbase/pyseekdb.git
+cd pyseekdb
+
+# Install dependencies (all groups)
+make install
+```
+
+## Make Targets
+
+```bash
+make help                      # Show all available targets
+make install                   # Install dependencies
+make test                      # Run unit tests
+make test-integration-embedded # Run embedded integration tests
+make docs                      # Build documentation
+make demo                      # Run RAG demo
+make build                     # Build the package
+make clean                     # Clean build artifacts
+```
+
+## Build Artifacts
+
+After running `make build`, the distribution files will be in the `dist/` directory:
+- `pyseekdb-<version>.tar.gz` - Source distribution
+- `pyseekdb-<version>-py3-none-any.whl` - Wheel distribution
+
+## Testing
+
+```bash
+# Run unit tests
+make test
+
+# Run embedded integration tests
+make test-integration-embedded
+
+# Run specific tests with uv run
+uv run pytest tests/integration_tests/ -v -k "server"     # server mode (requires seekdb server)
+uv run pytest tests/integration_tests/ -v -k "oceanbase"  # oceanbase mode (requires OceanBase)
+
+# Run specific test file
+uv run pytest tests/integration_tests/test_collection_query.py -v
+
+# Run specific test function
+uv run pytest tests/integration_tests/test_collection_query.py::TestCollectionQuery::test_collection_query -v
+```