Add statement "how to contribute" to readme.md

How to Contribute

We welcome contributions to our project! To get started:

• Fork the repository.
• Create a new branch for your feature or bug fix.
• Write clear, maintainable code with appropriate tests.*
• Submit a pull request with a detailed description of your changes.

(* All contributions are required to pass the following list of tests, automated in GitLab pipelines: ...)

Please follow our coding standards and guidelines. We appreciate your help in making this project better!