Document Task(f, n) API (#55184)

Fixes #55005 and helps work
around issues discussed in
#54998.

base/docs/basedocs.jl

@@ -1835,12 +1835,15 @@ Stacktrace:
 DomainError
 
 """
-    Task(func)
+    Task(func[, reserved_stack::Int])
 
 Create a `Task` (i.e. coroutine) to execute the given function `func` (which
 must be callable with no arguments). The task exits when this function returns.
 The task will run in the "world age" from the parent at construction when [`schedule`](@ref)d.
 
+The optional `reserved_stack` argument specifies the size of the stack available
+for this task, in bytes. The default, `0`, uses the system-dependent stack size default.
+
 !!! warning
     By default tasks will have the sticky bit set to true `t.sticky`. This models the
     historic default for [`@async`](@ref). Sticky tasks can only be run on the worker thread