Documentation

Mathlib.Data.Array.Lemmas

Porting note: Following the discussion on [Zulip](https://leanprover.zulipchat.com/#narrow/stream/287929- mathlib4/topic/porting.20.60.2Earray.60.20files.20whose.20PR's.20were.20closed.3F), these will wait until Batteries has finalized DArray and Array' types so we can translates apples to apples.

align for lemmas about lean3/mathlib3 versions of d_array and array with mathport output