[joss][docs] Developer docs

[sneakers-the-rat]

Part of: openjournals/joss-reviews#6336

Collecting ideas for developer docs here rather than in separate issues. Trying to minimize nags and only focus on things that I think would be helpful for inviting contributors and allowing for maintenance

• How to run tests? (looks pretty standard, npm install && npm run test)
• Expectations for contributions in Contributing.md - "test new functionality, run tests, etc."
• ... (will update as i continue to read)

[katjaq]

Thank you! We have now added to the Contributing.md in commit 6e74c28:

Test new functionalities

If you would like to change the code, please make sure the existing tests run using npm install && npm run test.
If you add a new functionality, please also implement new test(s) to make sure of its correct working. Thank you.

[sneakers-the-rat]

Fabulous! That's pretty much all i came up with as i was reading! feel free to close

[katjaq]

Great :) Thank you.