Instead of using the user's standard shell, this script should be run using...

Instead of using the user's standard shell, this script should be run using zsh, since that was the shell it was written for.  On my machine changes to my default shell only take effect when I log out and then long in again.  Plus, it's nice for people to be able to try oh-my-zsh out even if zsh isn't their default shell right?  :-)