docs: Streamline documentation, create CONTRIBUTING.md

- Slim README.md to essentials (intro, badges, install, links)
- Create CONTRIBUTING.md with:
  - Development setup (pixi and pip)
  - Test running instructions
  - Pre-commit hooks
  - Environment variables
  - Condensed docstring style guide
- Delete DOCSTRING_STYLE.md (merged into CONTRIBUTING.md)

README: 218 → 82 lines
All detailed docs now at docs.datajoint.com

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: dimitri-yatsenko

CONTRIBUTING.md

@@ -0,0 +1,152 @@
+# Contributing to DataJoint
+
+## Development Setup
+
+### Prerequisites
+
+- [Docker](https://docs.docker.com/get-docker/) (Docker daemon must be running)
+- [pixi](https://pixi.sh) (recommended) or Python 3.10+
+
+### Quick Start with pixi
+
+[pixi](https://pixi.sh) manages all dependencies including Python, graphviz, and test tools:
+
+```bash
+git clone https://github.com/datajoint/datajoint-python.git
+cd datajoint-python
+
+# Run tests (containers managed automatically)
+pixi run test
+
+# Run with coverage
+pixi run test-cov
+
+# Run pre-commit hooks
+pixi run pre-commit run --all-files
+```
+
+### Alternative: Using pip
+
+```bash
+pip install -e ".[test]"
+pytest tests/
+```
+
+---
+
+## Running Tests
+
+Tests use [testcontainers](https://testcontainers.com/) to automatically manage MySQL and MinIO containers. No manual `docker-compose up` required.
+
+```bash
+pixi run test                                    # All tests
+pixi run test-cov                                # With coverage
+pixi run -e test pytest tests/unit/              # Unit tests only
+pixi run -e test pytest tests/integration/test_blob.py -v  # Specific file
+```
+
+**macOS Docker Desktop users:** If tests fail to connect:
+```bash
+export DOCKER_HOST=unix://$HOME/.docker/run/docker.sock
+```
+
+### External Containers (for debugging)
+
+```bash
+docker compose up -d db minio
+DJ_USE_EXTERNAL_CONTAINERS=1 pixi run test
+docker compose down
+```
+
+### Full Docker
+
+```bash
+docker compose --profile test up djtest --build
+```
+
+---
+
+## Pre-commit Hooks
+
+Hooks run automatically on `git commit`. All must pass.
+
+```bash
+pixi run pre-commit install              # First time only
+pixi run pre-commit run --all-files      # Run manually
+```
+
+Hooks include: **ruff** (lint/format), **codespell**, YAML/JSON/TOML validation.
+
+---
+
+## Before Submitting a PR
+
+1. `pixi run test` — All tests pass
+2. `pixi run pre-commit run --all-files` — Hooks pass
+3. `pixi run test-cov` — Coverage maintained
+
+---
+
+## Environment Variables
+
+For `DJ_USE_EXTERNAL_CONTAINERS=1`:
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `DJ_HOST` | `localhost` | MySQL hostname |
+| `DJ_PORT` | `3306` | MySQL port |
+| `DJ_USER` | `root` | MySQL username |
+| `DJ_PASS` | `password` | MySQL password |
+| `S3_ENDPOINT` | `localhost:9000` | MinIO endpoint |
+
+---
+
+## Docstring Style
+
+Use **NumPy-style** docstrings for all public APIs:
+
+```python
+def insert(self, rows, *, replace=False):
+    """
+    Insert rows into the table.
+
+    Parameters
+    ----------
+    rows : iterable
+        Rows to insert. Each row can be a dict, numpy record, or sequence.
+    replace : bool, optional
+        If True, replace existing rows with matching keys. Default is False.
+
+    Returns
+    -------
+    None
+
+    Raises
+    ------
+    DuplicateError
+        When inserting a duplicate key without ``replace=True``.
+
+    Examples
+    --------
+    >>> Mouse.insert1({"mouse_id": 1, "dob": "2024-01-15"})
+    """
+```
+
+### Section Order
+
+1. Short summary (one line, imperative mood)
+2. Extended description
+3. Parameters
+4. Returns / Yields
+5. Raises
+6. Examples (strongly encouraged)
+7. See Also
+
+### Style Rules
+
+- **Do:** Imperative mood ("Insert rows" not "Inserts rows")
+- **Do:** Include examples for public APIs
+- **Don't:** Document private methods extensively
+- **Don't:** Repeat function signature in description
+
+See [NumPy Docstring Guide](https://numpydoc.readthedocs.io/en/latest/format.html) for full reference.