Zsh for iSH - spaceshiptrip/iOS-stuff GitHub Wiki
You can install zsh:
apk add zsh
Then download oh-my-zsh: sh -c "$(wget https://raw.github.com/ohmyzsh/ohmyzsh/master/tools/install.sh -O -)"
Change the default shell through:
vim /etc/passwd
Then change the root shell to /bin/zsh