docs: Explain how to contribute

CONTRIBUTING.md

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+# Contributing Guidelines
+
+Thank you for taking the time to contribute to the `fr-format` project! Your help is greatly appreciated.
+
+## How to Contribute ?
+
+We welcome all forms of contributions,they are highly encouraged: 
+
+* Submitting Pull Requests (Enhancing code, Improving or adding documentation)
+* Reporting Issues or suggesting improvements
+
+For more details, follow the sections below.
+
+### Submitting Pull Requests
+
+#### Enhancing code
+
+Please follow these important steps to contribute effectively to the project:
+
+1. Clone the project repository and navigate to `fr-format` folder.
+2. Insure you have Poetry installed by running `poetry --version`. If not, [install Poetry](https://pypi.org/project/poetry/).
+3. Check your Python version matches the required version specified in `pyproject.toml`.
+4. Run `poetry install` to create a virtual environment and install all dependencies.
+5. Activate the virtual environment using `poetry shell`.
+6. Use the `Makefile` for predefined tasks. Run `make help` to see available commands.
+
+##### Adding features or fixing bugs
+
+At first, ensure you are working with the latest version of the project: `git pull origin main`.
+
+After verification, follow these steps: 
+
+1. Create a new branch for your feature or fix: `git checkout -b feature-name`.
+2. Implement your changes and test them :
+   - Run `make test` to execute tests.
+   - Use `make lint` to ensure your code follows the project's style guidelines.
+3. Document your changes:
+   - Provide a clear explanation in your pull request description.
+   - Add comments to your code if necessary. 
+
+6. Finally, submit your pull request and tag relevant contributors for review .
+
+##### Suggesting a new french format (Main feature)
+
+Before adding a new format, please verify at first these two points before creating the pull request appropriate to this feature:
+
+1. Check the [list of available formats](./docs/formats.md) to ensure it doesn't already exist.
+2. Be sure that the new format is relevant, meaningful and specifically French. 
+
+After verification, these are the steps to add it:
+
+1. Create a file to store validated data values(If the data list is large)
+2. Create a second one to implement the format validation logic. (You can take examples from the existing code)
+3. Test it!
+4. Fix Linting problems running `make lint-fix`.
+5. Import the format inside `./src/frformat/__init__`.
+6. Add it to `all_formats` list. 
+7. Run `make generate-docs` to update the format documentation. 
+The aim of this step is to save all formats inside one table to be more clear for users.
+
+#### Improving and adding documentation
+
+All documentation files are located in [docs folder](./docs).\
+If your changes include complex logic or functionality, add clear and concise doc comments to explain them.
+Also, if you identify areas for improvement in the [README file](./docs/dev/README.md), other documentation files, or even files without existing documentation where an explanation would add value, please contribute, it's highly encouraged!
+
+**Note**: If you are adding a new french format to the project, remember to run `make generate-docs` to update the documentation and refresh the list of all available formats.
+
+### Reporting Issues or suggesting improvements
+
+If you encounter a bug or have a suggestion, please:
+
+1. Ensure you are using the latest version of the project and verify if updating fixes your issue first.
+2. Check if the issue already exists in the [Github Issues section](https://github.com/datagouv/fr-format/issues) (please do not open a duplicate one !).
+3. Provide a detailed issue report is very appreciate!\
+   Including:\
+              - A clear description of the problem or suggestion.\
+              - Steps to reproduce the bug (if applicable).\
+              - Any relevant logs or screenshots.
+
+## Code Style Guidelines
+
+`fr format` projevt uses the following linting and formatting dependencies:
+- [Black](https://black.readthedocs.io/en/stable/)
+- [Isort](https://pycqa.github.io/isort/)
+- [Flake8](https://flake8.pycqa.org/)
+- [Pyright](https://github.com/microsoft/pyright)
+
+These tools are installed automatically when you run `poetry install` after forking the project.\
+Before submitting your code, run `make lint` to check for linting issues and fix them using `make lint-fix`.
+
+## License
+
+By contributing to `fr-format`, you agree that your contributions will be licensed under the project's open-source license: MIT.
+
+Thank you for your contribution !
+
+
+