The documentation on releases that you find via a google-search or just manually navigating to docs.buildbot.net dont mention anything about a move to github for 'further' releases/release-notes.
It turns out there are two new releases after 3.6.0 I had no inkling of, no mention was made of them on the website.
I would suggest at least adding a reference somewhere that certain parts (releasenotes, versions, ....others?) have moved to Github.
I've had a babylonian misunderstanding with a colleague due to him landing on Github for his info, and me searching the official website docs for info.