Document custom ordination process

We have all the components (rarefaction, consolidation at family level, `prcomp` calls to get loadings, etc) needed to make a nice little helper function that does all the work, but those are also the steps that a user may want to do differently for their ordination. We don't have to come up with every possible parameter ahead of time for a helper function if we just provide an example script highlighting areas someone may want to tweak.