Update latest.md

Initial PR for updating link to docs re issue (on openbadges repo) https://github.com/mozilla/openbadges/issues/1013

At this point I'm pretty clueless about the spec but would hope to give the docs an overhaul when I have more of a clue.. :wink: I'm guessing the docs in both this repo and the openbadges one could both benefit from some updates at that point, so can add more commits to this PR or create new ones as and when..