update ChangeLog

ChangeLog

 Changes since NIFTy 5:
 
+New approach for random number generation
+=========================================
+
+The code now uses `numpy`'s new `SeedSequence` and `Generator` classes for the
+production of random numbers (introduced in numpy 1.17. This greatly simplifies
+the generation of reproducible random numbers in the presence of MPI parallelism
+and leads to cleaner code overall. Please see the documentation of
+`nifty6.random` for details.
+
 Interface Change for non-linear Operators
 =========================================
 
@@ -17,7 +26,6 @@ behaviour since both `Operator._check_input()` and
 `extra.check_jacobian_consistency()` tests for the new conditions to be
 fulfilled.
 
-
 Special functions for complete Field reduction operations
 =========================================================