Document our downloads.json file
We have https://aus1.torproject.org/torbrowser/update_3/release/downloads.json (and a similar URL for alpha (s/release/alpha)) for users/devs that want to keep a reliable way for grabbing the latest updates or pull the latest version information so that they can see when new updates are available.
The JSON file got specifically created to be easily parsable in #16651 (moved). This seems to work pretty well from all we know but we never documented that feature nor specified it.
We think this should finally be mentioned on our dev portal and we should write kind of a retroactive proposal and put it into our proposal folder in
tor-browser-spec so that we have something official we can link to.