Added docstring for Artifacts.jl (JuliaLang#52913)

This is a part of issue JuliaLang#52725.

---------

Co-authored-by: Steven G. Johnson <[email protected]>
Co-authored-by: Max Horn <[email protected]>
(cherry picked from commit 15e2af2)

Author: 3 people

stdlib/Artifacts/test/runtests.jl

@@ -164,3 +164,7 @@ end
     @test length(Base.manifest_names) == n
     @test length(Base.preferences_names) == n
 end
+
+@testset "Docstrings" begin
+    @test isempty(Docs.undocumented_names(Artifacts))
+end