Proposal: Adding a CONTRIBUTING.md file to streamline the contribution process

[GabrielBaiano]

Hi @johnfactotum and community!

I’m a big fan of Foliate and I’ve been looking into ways to help the project grow. One thing I noticed is that we currently don't have a centralized CONTRIBUTING.md file.

As the project gains more traction, having a clear "onboarding" guide for new developers would be incredibly beneficial. My suggestion is to create a document that covers:

Development Environment Setup: Clear instructions on dependencies (GJS, GTK4/Libadwaita, WebKitGTK) and how to build the project using Meson/Ninja.

Code Style & Guidelines: Ensuring consistency across the codebase for new Pull Requests.

Workflow: Best practices for opening issues, reporting bugs, and submitting features.

Translation Guide: Brief instructions on how to contribute to the app's localization.

I believe this would lower the barrier for entry for new contributors and save time for maintainers by ensuring PRs follow the project's standards from the start.

I’d be happy to draft a first version (PR) for this document if you agree with the idea. What do you think?