Shell hook needs to work if user already has a chdir shell hook

[mxcl]

Need thoughts on this, though I think we can release without solving it and see what happens.

[jhheider]

https://github.com/rothgar/mastering-zsh/blob/master/docs/config/hooks.md#add-function-to-hook

[jhheider]

    echo >> ~/.zshrc
    echo '# added by tea' >> ~/.zshrc
    echo 'tea-chpwd() { source <(tea -Eds) }' >> ~/.zshrc
    echo 'add-zsh-hook -Uz chpwd tea-chpwd' >> ~/.zshrc

most likely.