No docs for positive_ordered vector constraint transform

[spinkney]

It's an easy fix as the unconstrained $y$ is first constrained to be positive and then the ordered vector constraint is applied.

[bob-carpenter]

I think @spinkney is requesting a section in the transforms chapter of the reference manual:

https://mc-stan.org/docs/reference-manual/variable-transforms.html

It should follow the other sections and the transform is exactly as @spinkney describes.

My bad for missing this one in the first place!