Outdated mailing list

[Pavel Rappo]

README.md has this line:

> concurrency-interest at cs.oswego.edu: general discussion on concurrency

The bad news is that this list is no longer available. The good news
is that there's a substitute [^1]:

> concurrency-discuss at openjdk.org: General discussion about concurrency topics (e.g. java.util.concurrent API)

[^1]: https://mail.openjdk.org/pipermail/core-libs-dev/2024-August/127856.html