Guide for new ActivityPub implementers

@Sebastian thx! I’ve done a first pass at redrafting as three guides. I’ve also pulled out most of what was in the section “Potential models and building blocks”. Instead I’ve pointed to some places to discover ActivityPub implementations and I’ll open an issue on Fediverse.Party to add in the projects I’d compiled that aren’t there already.

I’d like to start figuring out some next steps. If this is potential content for the draft activitypub.rocks improvements, how do we get from here to there? Maybe we need a documentation team? Maybe there is one already? In any case, I’d be happy to participate.