Rewrite CONTRIBUTORS.md

[booyaa]

Brief

The goal is to make it easier for people to start helping, with the emphasis being less on coding skills or expertise in Rust.

Update this document (CONTRIBUTORS.md) to explain how to get started with the project i.e. pick one of the issues labelled help wanted and good first issue.

Explain the difference between no code and code.

Also mention that mentoring is provided for all issues.

You can find a brief description of these labels here.

Important: you don't need to extract a list of outstanding issues, just provide a filtering link to said label e.g. good first issue would be good first issue Good for newcomers, usally co-tagged with easy

Hint

For inspiration the rather excellent document written for STEMMRoleModels!

Mentor: (insert name or delete if not required)

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Mentoring can be provided, just ask.
Please add comment if you are claiming this issue so we can assign it to you.