Guide for new ActivityPub implementers

It might make sense. It should be part of some more effort to turn this into a high quality chunk of documentation. It needs a process then, and people dedicating to it. Right now I think most people do not realize that the top post is a wiki that they can freely update, and are even encouraged to do so.

An improvement to this documentation process isn’t useful if at the same time @gabek and @j12t are coordinating the fedidevs.org initiative that intends to do the same. Hence I mentioned the “Fediverse Developer Documentation Website” bullet point in the wiki about organizing for more cohesion of initiatives.