Update asyncmap docs to clarify order of outputs (#54974)

Author: haakon-e

base/asyncmap.jl

@@ -9,6 +9,8 @@ Uses multiple concurrent tasks to map `f` over a collection (or multiple
 equal length collections). For multiple collection arguments, `f` is
 applied elementwise.
 
+The output is guaranteed to be the same order as the elements of the collection(s) `c`.
+
 `ntasks` specifies the number of tasks to run concurrently.
 Depending on the length of the collections, if `ntasks` is unspecified,
 up to 100 tasks will be used for concurrent mapping.