git clone https://github.com/sstephenson/rbenv.git ~/.rbenv

(.bashrc/.zshrc already taken care of in .shellrc)

git clone https://github.com/sstephenson/ruby-build.git ~/.rbenv/plugins/ruby-build

(may also want the rehash plugin rbenv-gem-rehash) rbenv-gem-rehash has been integrated into rbenv core, woop.