Yeah, I just had to search for this because I thought, I missed that too!

git() {
  if [ "$1" = "cd" ]; then
    shift
    cd "./$(command git rev-parse --show-cdup)$*"
  else
    command git "$@"
  fi
}

This lets you run git cd to go to the root of your repo, or git cd foo/bar to go to a path relative to that root. You can’t do it as an alias because it’s conditional, and you can’t do it as a git-cd command because that wouldn’t affect the current shell.