chore(contributing): add CONTRIBUTING guide

CONTRIBUTING.md

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+# How to Contribute
+
+## Pull Requests
+
+Repository use the [GitHub flow](https://guides.github.com/introduction/flow/) as main versioning workflow
+
+1. Fork the repository
+2. Create a new branch for each feature, fix or improvement
+3. Keep your git history as clean as possible
+4. Send a pull request from each feature branch to the **master** branch
+
+It is very important to separate new features or improvements into separate feature branches, and to send a
+pull request for each branch.
+
+This allow us to review and pull in new features or improvements individually.
+
+## Style Guide
+
+All pull requests SHOULD adhere to the [Conventional Commits specification](https://conventionalcommits.org/)
+
+## License
+
+You must agree that your patch will be licensed under the MIT License, and when we change the license we will assume that you agreed with the change unless you object to the changes in time.