These instructions were obtained by installing the latest node which outputs the actual yarn instructions right at the end:
## To install the Yarn package manager, run:
curl -sL https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add –
echo “deb https://dl.yarnpkg.com/debian/ stable main” | sudo tee /etc/apt/sources.list.d/yarn.list
sudo apt-get update && sudo apt-get install yarn