Add note about @threads threadpool (#59802)

(cherry picked from commit a817940)

Author: IanButterworth

base/threadingconstructs.jl

@@ -287,8 +287,14 @@ A macro to execute a `for` loop in parallel. The iteration space is distributed
 coarse-grained tasks. This policy can be specified by the `schedule` argument. The
 execution of the loop waits for the evaluation of all iterations.
 
+Tasks spawned by `@threads` are scheduled on the `:default` threadpool. This means that
+`@threads` will not use threads from the `:interactive` threadpool, even if called from
+the main thread or from a task in the interactive pool. The `:default` threadpool is
+intended for compute-intensive parallel workloads.
+
 See also: [`@spawn`](@ref Threads.@spawn) and
 `pmap` in [`Distributed`](@ref man-distributed).
+For more information on threadpools, see the chapter on [threadpools](@ref man-threadpools).
 
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