$ yaourt -S zsh aur/oh-my-zsh-git

Run for the first time, zsh will prompt for configuration. Just ignore it, because we could use oh-my-zsh to help later.

$ zsh

Here is how oh-my-zsh to comes to help:

$ cp /usr/share/oh-my-zsh/zshrc ~/.zshrc
$ chsh -s $(which zsh)