docs: add CONTRIBUTING.md

Author: davidB

CONTRIBUTING.md

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+# Contributing
+
+Every contribution is welcome!
+
+By contributing to this project, you agree to the [Contributor License Agreement (CLA)](https://cla-assistant.io/cdviz-dev/transformers-community).
+
+## How to contribute
+
+### Reporting bugs
+
+If you found a bug, please open an [issue].
+
+### Suggesting enhancements
+
+If you have an idea for an enhancement, please open an [issue].
+
+### Contributing documentation
+
+If you want to contribute documentation, please open a pull request, and start a discussion on the PR.
+
+### Contributing code
+
+If you want to contribute code, please open an [issue] first to discuss what you want to do. Do not open a new [issue] to work on an existing [issue]. Then fork the repository, create a branch, and open a pull request.
+
+1. Fork the repository.
+2. Create a branch for your changes.
+3. Commit with `git commit -s` to sign off your work.
+4. Submit a pull request.
+
+All contributions must include a `Signed-off-by` line.
+
+## How to build
+
+The repository is composed of multiple subfolders / modules.
+
+### Prerequisites
+
+- [mise-en-place](https://mise.jdx.dev/) to download tools, setup local environment (tools, environment variables) and to run the tasks
+- [docker](https://docs.docker.com/get-started/) to run the containers and to execute some tests.
+  To build the container locally you have to configure the container image store
+  (see [Multi-platform | Docker Docs](https://docs.docker.com/build/building/multi-platform/#prerequisites)
+  & [containerd image store | Docker Docs](https://docs.docker.com/engine/storage/containerd/))
+
+### Build
+
+```bash
+mise install
+
+# to have list of tasks
+mise tasks
+
+# to run a task
+mise run {{task}}
+
+# to run the CI tasks
+mise run ci
+```
+
+## How to test
+
+```bash
+mise run test
+```
+
+## How to release
+
+???
+
+[issue]: https://github.com/cdviz-dev/cdviz-collector/issues "CDviz collector's issue tracker"