[stephencelis]

  If you want to set your login shell to zsh, go to System 
  Preferences -> Users and Groups. Right-click on your user 
  account and select Advanced Options. Change the login shell 
  dropdown to /bin/zsh.

You're better off using `chsh -s /bin/zsh` (or, better yet, `brew install zsh`, append `/usr/local/bin/zsh` to `/etc/shells`, and use that, instead).