Merge pull request #111 from hendo-21/docs/contributing

docs(contributing): improve dev environment setup instructions

Author: blkdmr

CONTRIBUTING.md

@@ -37,13 +37,19 @@ When you make changes, aim to:
 - Add or update tests and documentation if your change affects behavior or public APIs.
 - Keep commits logically grouped (for example, separate “refactor” from “new feature” where it makes sense).
 
-**Please note** that, in order to test your changes, you need to reinstall `fenn` locally in editable mode by running:
+**Please note** that, in order to test your changes, you need to reinstall `fenn` locally in editable mode along with its dev and test dependencies. `fenn` uses pre-commit and ruff for automated linting and formatting. From the base project directory (the one containing the project `pyproject.toml` file), run:
 
 ```
-pip install -e .
+pip install -e ".[dev,test]"
 ```
 
-from the base project directory (the one containing the project `pyproject.toml` file).
+### Set up pre-commit hooks
+
+Run `pre-commit install` to wire up the pre-commit git hook. This only needs to be done once after cloning your fork.
+
+This makes pre-commit run the configured hooks (`ruff check` and `ruff format` currently) on every `git commit`. Your commit may be blocked if a hook reports a failure or modifies a file. `ruff format` may reformat your code automatically, so you'll need to review the modifications and stage them again before committing. Without this step your commits may fail CI.
+
+See the [`ruff` documentation](https://docs.astral.sh/ruff/) for more information.
 
 Once your branch is ready: