Contributing session with access and workflow

[nitrosx]

This PR updates the contributing section which now includes who can access what and a visualization of the workflow

[ddijken]

Thanks for putting this together! The contribution workflow is much clearer already!

I think my earlier comments may have been about a different layer. What I was referreing to is documentation one level above the PR workflow: what happens after the steering committee decides on a feature? For example: how is a project lead assigned, what deliverables are they accountable for, and what does the timeline look like? Having that written down would make the coordination much easier and easier to escalate if things slip.