Add contribution guidelines for external contributors & translators

Content request

✏ Suggest ideas for new content!

Checklist

• This issue is not a duplicate, I've searched the Issue Tracker
• This issue is not a question, I'm aware that I can submit questions via Mastodon, Twitter, Email, Reddit or Matrix
• This issue is a content request, and not a bug report, feature request, or anything other

What are you missing or what could be improved?

Add clear contribution guidelines for people who want to get involved with the project.

What is the solution you'd like to see?

Clear guidelines on:

1. how to ask questions or join community discussions
2. how to open an Issue (content requests, feature requests, bug reports)
3. how to work on Issues (forking, branching, submitting merge request)
4. donations

Do you have additional comments?

N/A