add concrete example to NEWS

Author: mbauman

NEWS.md

@@ -40,7 +40,9 @@ Standard library changes
 
 * Empty dimensional reductions (e.g., `reduce` and `mapreduce` with the `dims` keyword
   selecting one or more dimensions) now behave like their whole-array (`dims=:`) counterparts,
-  only returning values in unambiguous cases and erroring otherwise.
+  only returning values in unambiguous cases and erroring otherwise. For example,
+  `minimum([], dims=2)` is now an error; it would previously return an empty array.
+  This can be addressed with the `init` keyword argument as the error message directs.
 
 #### JuliaSyntaxHighlighting