Add release documentation for the docs component

An attempt to define how we do releases of the docs component. I tried to keep it out of scope to check interoperability from a "content perspective", which is something the collection release / processes nearby the manifest should take ownership of. So here, we're just looking to see that we're able to build a site that's coherent and working; so that there will be no surprises later when a collection release is being cut.

Part of #50 (closed).