No detailed Apicalyse documentation

[forana]

(I realize this isn't really for this repo, but I'm hoping the right people who can fix this issue see this)

https://apicalypse.io/ links to https://github.com/igdb/apicalypse-docs, which does not exist. This means that, aside from the small "cheatsheet" in the IGDB docs (which seems to duplicate the content on https://apicalypse.io/syntax/), there is no detailed documentation for the Apicalypse format.