Reword layout for arrays to reduce potential indexing confusion.

Author: owengage

src/type-layout.md

@@ -70,10 +70,9 @@ at least equal to the size and alignment of a pointer.
 
 ## Array Layout
 
-Arrays are laid out so that the `nth` element of the array is offset from the
-start of the array by `(n-1) * the size of the type` bytes i.e. the `1st` 
-element has an offset of 0. An array of `[T; n]` has a size of 
-`size_of::<T>() * n` and the same alignment of `T`.
+An array of `[T; N]` has a size of `size_of::<T>() * N` and the same alignment
+of `T`. Arrays are laid out so that the zero-indexed `n`th element of the array
+is offset from the start of the array by `n * size_of::<T>()` bytes.
 
 ## Slice Layout