document AbstractArray and doctest for Array (#22052)

Author: fredrikekre

base/abstractarray.jl

@@ -2,6 +2,13 @@
 
 ## Basic functions ##
 
+"""
+    AbstractArray{T, N}
+
+Abstract array supertype which arrays inherit from.
+"""
+AbstractArray
+
 """
     size(A::AbstractArray, [dim...])
 

base/array.jl

@@ -53,10 +53,22 @@ import Core: arraysize, arrayset, arrayref
     Array{T,N}(dims)
 
 Construct an uninitialized `N`-dimensional dense array with element type `T`,
-where `N` is determined from the length or number of `dims`.  `dims` may
+where `N` is determined from the length or number of `dims`. `dims` may
 be a tuple or a series of integer arguments corresponding to the lengths in each dimension.
 If the rank `N` is supplied explicitly as in `Array{T,N}(dims)`, then it must
 match the length or number of `dims`.
+
+# Example
+
+```jldoctest
+julia> A = Array{Float64, 2}(2, 2);
+
+julia> ndims(A)
+2
+
+julia> eltype(A)
+Float64
+```
 """
 Array