Add federation.md ?
SocialHub came with a format to describe activities support for different implementations in a human readable way (nodeinfo already being the machine-readable one). https://socialhub.activitypub.rocks/t/documenting-federation-behavior-in-a-semi-standard-way/453/6
I'm quite interested in having it in pleroma but it is quite a long document that would need maintenance so I want your opinions on it.