Review of `CONTRIBUTING.md` needed

[geoffreygarrett]

Hi everyone, I put together a CONTRIBUTING.md that we can use in the meantime, adapted from a template which was aligned with our workflow. Feel free to make any further modifications!

[geoffreygarrett]

If I missed anyone here, please add them!

[DominicDirkx]

@jgte How much does this overlap with what you have/will prepare?

[jgte]

I've have a look at it tomorrow.

[FilippoOggionni]

I can take care of this in parallel with the updates to the developer docs. As agreed during the developer meeting, I will use the draft I posted on Slack and include it in this file

[jgte]

Sorry I didn't get around to this yesterday