I would suggest not to follow that tutorial. For some reason the tutorial clones NodeBB under /var/www which is not required. Also you will end up using the master branch of NodeBB which is a development version and is likely to have bugs.

+1 for a direct link. I guess the most direct at the moment is via github (pricing -> github -> Documentation & Installation Instructions) o_O . docs.nodebb.org <-- now it's in mine too