announce new tor-browser-bundle releases
Tor stable releases are announced on tor-announce . Tor alpha releases are announced via tor-talk .
The recent security updates to TBB make clear that keeping the userbase informed about new releases especially on the client site is crucial for security and anonymity. Therefore I would suggest to create torbrowser-announce. I thinks a separate mailing-list is better because this reduces the noise for someone only trying to monitor new TBB releases while not being interested in general tor-talk.
TBB users are also informed via the default startpage, but not everyone uses the default page and in some cases the admins responsible for deploying updates don't use TBB themself (or read blog.tpo).