docstring update

src/experimental.jl

@@ -8,6 +8,9 @@ Specifically, a task can only pass the `@barrier` if `n-1` other tasks have reac
 as well. The value of `n` is determined from `@set ntasks=...`, which
 is required if one wants to use `@barrier`.
 
+Because this feature is experimental, it is required to load `@barrier` explicitly, e.g. via
+`using OhMyThreads.Experimental: @barrier`.
+
 **WARNING:** It is the responsibility of the user to ensure that the right number of tasks
 actually reach the barrier. Otherwise, a **deadlock** can occur. In partictular, if the
 number of iterations is not a multiple of `n`, the last few iterations (remainder) will be