[isabelle-dev] Build NEWS

[Lars Hupel]

> Maybe this can be simplified further. The "slow" group in the main
> Isabelle repository is now rather pointless, even counterproductive.
> HOL-Proofs and its subsessions has become relatively fast compared to
> other bulky sessions.
> 
> E.g. Isabelle/65f279853449 on 12 cores with 6 threads per ML process:
> 
> build -j4 -a
> 0:27:21 elapsed time, 7:13:18 cpu time, factor 15.84

Thanks for that observation. This is now rectified in Isabelle/d0dfdd413a7f.

Cheers
Lars