docs: add usage example and dev file

DEVELOPMENT.MD

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+# python-dcm230
+
+Driver for Eastron DCM230 DC Energy Meters using Modbus RTU.
+
+## Get started
+
+### Prerequisites
+
+* Install [Python (>=3.10)](https://www.python.org/downloads/)
+* Install [git](https://git-scm.com/downloads)
+* Install [uv](https://docs.astral.sh/uv/getting-started/installation/)
+
+### Setup development environment
+
+Clone the repository:
+
+```sh
+git clone git@github.com:id8-engineering/python-dcm230.git
+```
+
+Change directory:
+
+```sh
+cd python-dcm230
+```
+
+Run pre-commit tests:
+
+```sh
+uv run pre-commit run -a
+```
+
+Build package:
+
+```sh
+uv build
+```

README.md

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+[![OpenSSF Scorecard](https://api.scorecard.dev/projects/github.com/id8-engineering/python-dcm230/badge)](https://scorecard.dev/viewer/?uri=github.com/id8-engineering/python-dcm230)
+
+## python-dcm230
+
+python-dcm230 provides a simple, Pythonic interface for reading and writing data 
+from Eastron DCM230 DC meters over Modbus RTU. It builds on top 
+of [pymodbus](https://pypi.org/project/pymodbus/).
+
+## Example usage:
+
+```python
+from dcm230 import Dcm230
+from pymodbus.client import ModbusSerialClient
+
+# Configure the Modbus client
+client = ModbusSerialClient(
+   port="COM3",  # or "/dev/ttyUSB0" on Linux
+   baudrate=9600,
+   parity="E",
+   stopbits=1,
+   bytesize=8,
+   timeout=1,
+)
+
+# Device Modbus address
+device_address = 1
+
+# Initialize the Dcm230 driver
+meter = Dcm230(device_address=device_address, client=client)
+
+# Read voltage
+voltage = meter.V
+print(f"Voltage: {voltage} V")
+```
+
+## Report issues
+
+If you run into problems, you can ask for help in our [issue tracker](https://github.com/id8-engineering/python-dcm230/issues) on GitHub.
+
+## Contributing
+See [CONTRIBUTING.MD](https://github.com/id8-engineering/python-dcm230/blob/main/CONTRIBUTING.MD) and [DEVELOPMENT.MD](https://github.com/id8-engineering/python-dcm230/blob/main/DEVELOPMENT.MD).