My zsh config has three things:

    setopt PROMPT_SUBST ; PS1='[%n@%m %c$(__git_ps1 " (%s)")]\$ '
    bindkey "^R" history-incremental-search-backward
    autoload -Uz compinit && compinit

The first one is mentioned in `git-prompt.sh` that comes with git, which needs to be sourced as well.