Created a docstring for ntuple(f::F, ::Val{N}) (#32468)

* Created a docstring for ntuple(f::F, ::Val{N})

* Incorporate fredrikekre's suggestions

* Incorporated more suggestions into text.

* Added note about using integer input when N not known at compile time

* Update base/ntuple.jl

Co-authored-by: Takafumi Arakaki <takafumi.a@gmail.com>

* Update ntuple docstring to be more consistent with method signature

* Remove trailing whitespace in docstring

Co-authored-by: Viral B. Shah <ViralBShah@users.noreply.github.com>
Co-authored-by: Takafumi Arakaki <takafumi.a@gmail.com>

Author: 3 people

base/ntuple.jl

@@ -42,6 +42,23 @@ ntuple(f, ::Val{1}) = (@_inline_meta; (f(1),))
 ntuple(f, ::Val{2}) = (@_inline_meta; (f(1), f(2)))
 ntuple(f, ::Val{3}) = (@_inline_meta; (f(1), f(2), f(3)))
 
+"""
+    ntuple(f, ::Val{N})
+
+Create a tuple of length `N`, computing each element as `f(i)`,
+where `i` is the index of the element. By taking a `Val(N)`
+argument, it is possible that this version of ntuple may
+generate more efficient code than the version taking the
+length as an integer. But `ntuple(f, N)` is preferable to
+`ntuple(f, Val(N))` in cases where `N` cannot be determined
+at compile time.
+
+# Examples
+```jldoctest
+julia> ntuple(i -> 2*i, Val(4))
+(2, 4, 6, 8)
+```
+"""
 @inline function ntuple(f::F, ::Val{N}) where {F,N}
     N::Int
     (N >= 0) || throw(ArgumentError(string("tuple length should be ≥ 0, got ", N)))