Docs: Add contribution file to the project

[Sarrabah]

Goal

As outlined in issue #32, the aim of this PR is to create a CONTRIBUTING.md file that provides detailed guidance for developers on how to contribute effectively to the project.

Fix #32

[johanricher]

Looks good to me, great work! I would only suggest adding at the bottom of the format list a link titled "How to add a new format?" pointing to the related doc, since CONTRIBUTING.md is usually more for general guidelines rather than a specific or technical how-to, some people may not look for it there.

[Sarrabah]

Thank you @johanricher for your feedback! I just have one question please, when you said "pointing to the related doc," did you mean that you would prefer I add a link pointing to the section Implementing a new French format in the CONTRIBUTING.md file?

[johanricher]

I meant adding a link, at the bottom of the format list, to the CONTRIBUTING.md file (specifically the part explaining how to add a new format)