First make sure that you have NVM and Node.js installed.
curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.33.0/install.sh | bash
nvm install node
Then to install Gulp and all the plugins:
npm install
npm install -g gulp
Finally, to start developing, do:
gulp
To push changes to github pages use
gulp deploy
You'll probably want to install the Livereload extension on the Chrome app store too. If you just activate that extension, then it will talk to the Gulp Livereload server and auto-reload the page on SCSS/HTML changes. Super convenient for iterating!