Added Arrays low-level tutorial

Author: JordiManyer

deps/build.jl

@@ -30,6 +30,7 @@ files = [
   "Poisson with HHO on polytopal meshes"=>"poisson_hho.jl",
   "Block assembly and solvers: Incompressible Stokes example"=>"stokes_blocks.jl",
   "Lagrange multipliers" => "lagrange_multipliers.jl",
+  "Low-level API - Arrays"=>"arrays_dev.jl",
   "Low-level API - Poisson equation"=>"poisson_dev_fe.jl",
   "Low-level API - Geometry" => "geometry_dev.jl",
   "Low-level API - Custom ReferenceFEs" => "crouzeix_raviart_reffe.jl",