Make supported version timeline easier to find

I tried to find the timeline for support for tor versions. Places I looked:

https://gitweb.torproject.org/tor.git/tree/README https://gitweb.torproject.org/tor.git/tree/ReleaseNotes https://dist.torproject.org/ https://dist.torproject.org/README.old_versions https://lists.torproject.org/pipermail/tor-announce/2017-October/000143.html https://blog.torproject.org/new-stable-tor-releases-0318-03012-02913-02816-02515 https://blog.torproject.org/category/tags/stable-release https://blog.torproject.org/tor-0306-released-new-series-stable https://www.torproject.org/docs/faq.html.en https://encrypted.google.com/search?hl=en&q=tor%20long%20term%20support

I eventually found it at https://trac.torproject.org/projects/tor/wiki/org/teams/NetworkTeam/CoreTorReleases as I was documenting this ticket

Maybe this link could be put in the README, Changelog, ReleaseNotes, or the README on dist.tpo? (Or all/most of those?)