add release note

Author: mattip

doc/release/upcoming_changes/27147.performance.rst

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+* OpenBLAS on x86_64 and i686 is built with fewer kernels. Based on
+  benchmarking, there are 5 clusters of performance around these kernels:
+  ``PRESCOTT NEHALEM SANDYBRIDGE HASWELL SKYLAKEX``.
+
+* OpenBLAS on windows is linked without quadmath, simplfying licensing
+
+* Due to a regression in OpenBLAS on windows, the performance improvements
+  when using multiple threads for OpenBLAS 0.3.26 were reverted.