Add example for `reloo()`

We don't have an example in the docstring for `reloo()` currently because it was getting too complicated. We should add a comprehensive example here. I know that when I used `reloo()` in legacy ArviZ a while back, I had trouble implementing a proper sampling wrapper to actually use the function. I think it would be beneficial to develop a realistic, in-depth example for this to guide users in the right direction.

Start at the reloo() docstring and review how the function was used in legacy ArviZ, focusing on the sampling wrapper needed for a realistic example. Done means the docstring contains a comprehensive, in-depth example that guides users through a proper sampling wrapper and use of reloo().

Written by the indexing model from the issue text.