Triplot examples for (db)RDA

[antagomir]

RDA plots can indicate both features as well as covariates that influence ordination. Would be good to show examples in OMA, too.

Here some examples: https://stackoverflow.com/questions/32194193/plotting-rda-vegan-in-ggplot

Here some discussion on extracting feature scores: https://github.com/vegandevs/vegan/issues/254