docs: Restructure main README and extract CONTRIBUTING.md.

CONTRIBUTING.md

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+# Contributing
+
+This repository provides MicroPython drivers for the STeaMi board.
+The goal is to maintain a consistent, reliable, and maintainable codebase across all drivers.
+
+## Driver structure
+
+Each driver must follow this layout:
+
+```
+lib/<component>/
+├── README.md
+├── manifest.py
+├── <module_name>/
+│   ├── __init__.py
+│   ├── const.py
+│   └── device.py
+└── examples/
+    └── *.py
+```
+
+### Requirements
+
+* The directory name must match the driver name (e.g. `mcp23009e`, `wsen-hids`)
+* The main class must be exposed in `__init__.py`
+* Drivers must be self-contained (no cross-driver dependencies)
+
+## Coding conventions
+
+- **Constants**: use `from micropython import const` wrapper in `const.py` files.
+- **Naming**: `snake_case` for all methods and variables. Enforced by ruff (N802, N803, N806).
+- **Class inheritance**: `class Foo(object):` is the existing convention.
+- **Time**: use `from time import sleep_ms` (not `utime`, not `sleep()` with float seconds).
+- **Exceptions**: use `except Exception:` instead of bare `except:`.
+- **No debug `print()`** in production driver code.
+
+## Driver API conventions
+
+- **Constructor signature**: `def __init__(self, i2c, ..., address=DEFAULT_ADDR)` — first parameter is always `i2c` (not `bus`), address uses keyword argument with a default from `const.py`.
+- **Attributes**: `self.i2c` for the I2C bus, `self.address` for the device address (not `self.bus`, `self.addr`).
+- **I2C helpers**: use private snake_case methods `_read_reg()`, `_write_reg()` for register access.
+- **Device identification**: `device_id()` — returns the device/WHO_AM_I register value. All I2C drivers with an ID register must implement this method.
+- **Reset methods**: `reset()` for hardware reset (pin toggle), `soft_reset()` for software reset (register write), `reboot()` for memory reboot (reload trimming).
+- **Power methods**: `power_on()` / `power_off()`. All drivers must implement both.
+- **Status methods**: `_status()` returns the raw status register as an int (private), `data_ready()` returns True when all channels have new data, `<measurement>_ready()` for per-channel readiness (e.g. `temperature_ready()`, `pressure_ready()`).
+- **Measurement methods**: bare noun without unit suffix only for `temperature()` (°C) and `humidity()` (%RH). All others include the unit: `pressure_hpa()`, `distance_mm()`, `voltage_mv()`, `acceleration_g()`, etc. `read()` for combined reading returning a tuple, `<measurement>_raw()` for raw register values.
+- **Mode methods**: `set_continuous(odr)` to start continuous measurements, `trigger_one_shot()` for a single conversion, `read_one_shot()` for trigger + wait + return data.
+
+## Linting
+
+The project uses `ruff` for linting.
+
+```bash
+ruff check .
+```
+
+To automatically fix issues:
+
+```bash
+ruff check . --fix
+```
+
+## Commit messages
+
+Use the following format:
+
+```
+<scope>: <Description starting with a capital letter ending with a period.>
+```
+
+The scope is the driver name or domain (`hts221`, `ism330dl`, `docs`, `tests`, `ci`...). There is no predefined list of types — the scope is free-form.
+
+### Examples
+
+```
+hts221: Fix missing self parameter in get_av method.
+ism330dl: Add driver support for temperature reading.
+wsen-pads: Correct pressure conversion formula.
+docs: Update README driver table.
+tests: Add mock scenarios for mcp23009e driver.
+```
+
+## Workflow
+
+1. Create a branch from main (`git checkout -b my-new-feature`)
+2. Write your code and add tests in `tests/scenarios/<driver>.yaml`
+3. Run `ruff check` and `python -m pytest tests/ -v -k mock locally`
+4. Commit your changes following the commit message format
+5. Push your branch to the repository
+6. Open a Pull Request
+
+## Continuous Integration
+
+All pull requests must pass these checks:
+
+| Check | Workflow | Description |
+|-------|----------|-------------|
+| Commit messages | `check-commits.yml` | Validates commit message format |
+| Linting | `python-linter.yml` | Runs `ruff check` |
+| Mock tests | `tests.yml` | Runs mock driver tests |
+
+## Notes
+
+* Keep implementations simple and readable
+* Follow existing drivers as reference
+* Ensure documentation (`README.md`) and examples are included for each driver