Add whats-new

Author: hmaarrfk

doc/whats-new.rst

@@ -28,7 +28,7 @@ Performance
 
 - Small optimization to the netCDF4 and h5netcdf backends (:issue:`9058`, :pull:`9067`).
   By `Deepak Cherian <https://github.com/dcherian>`_.
-- Small optimizations to help reduce indexing speed of datasets (:pull:`9002`).
+- Small optimizations to help reduce indexing speed of datasets (:pull:`9002`, :pull:`9003`).
   By `Mark Harfouche <https://github.com/hmaarrfk>`_.