It is definitely possible to add a website to any OSM element in a full-featured OSM editor like JOSM or Vespucci, though they have quite a learning curve. It most likely isn't possible in Organic Maps. And a park, being a two-dimensional shape, is almost never represented as an OSM node, which is a single point. It's usually represented with an area, which is a type of way. This allows showing the shape and boundaries of the park.

Anyway, I added the French website (click on English in the top right corner of the webpage to switch to the English version), Wikipedia article, and an English name to the Montreal Botanical Garden. It will probably take at least a month or two to get into Organic Maps.