Add CONTRIBUTING.md

[amad-person]

We can add a CONTRIBUTING.md for MarkBind so that it becomes easier for new contributors to get started with our project.

This is a template we can use to get started.

Off the top of my head, good things to mention would be:

• what kind of contributions we're looking for (issues, PRs, etc.)
• how we make PRs (forking workflow)
• rules to follow for PRs (maybe a checklist for reminding contributors to run tests, follow our code style conventions, update documentation, etc.)

[yash-chowdhary]

Currently, in the developer guide, we have a large chunk of content (the Development Process heading) that can be used in the contributing.md file, while more stuff can be added.

Is the idea to link the contributing guidelines from the main page of the dev docs (as done in gatsby)?

[yamgent]

CONTRIBUTING.md should be more of a beginner's guide for contributors. The stuff in Development Process are more towards setting up the development environment, which is more of the practical side of things. CONTRIBUTING.md should instead be introducing to the open source nature of the repo. So for the gatsby example it should be something like this page.

This page has a pretty rough guide on how to write one: https://mozillascience.github.io/working-open-workshop/contributing/.