Unfortunately the old link is not available anymore, but I found the new instructions here: http://sharp.pixelplumbing.com/en/stable/install/#freebsd
Just in case that it's going down again, here are the short instructions which are missing in the FreeBSD install documentation of NodeBB ( https://docs.nodebb.org/installing/os/freebsd/ )
pkg install -y pkgconf vips
cd /usr/ports/graphics/vips/ && make install clean
I had to add DISABLE_VULNERABILITIES=yes to the end of the last command, because of some outdated dependency in the port. AFAIK the vips package is only used during installation or upgrade of NodeBB, so that shouldn't be any security issue.