Add guides for contributing for beginners

[bennyvasquez]

As mentioned in #544 , we could hugely benefit from a beginner guide on how to contribute to the wiki. I'd say either one for codespaces (as suggested by @GrooveCS) or a beginner guide to Git/Github (how to fork, how to make changes, then commit them, then create a pull request, and then what you do to get back to a clean environment).

[alaurie]

I could add devcontainer support to the repo with prettier and markdownlint installed automatically for codespaces.