docs: Honour $ZDOTDIR in code examples.
docs: Honour $ZDOTDIR in code examples.

Keep references in prose as '~/.zshrc': using $ZDOTDIR in that context would
be confusing, and people who set $ZDOTDIR understand these references.

psprint/zsh-syntax-highlighting,joshuarubin/dotfiles,x-way/zsh-syntax-highlighting,joshuarubin/dotfiles,joshuarubin/dotfiles,danielshahaf/zsh-syntax-highlighting-debian,zsh-users/zsh-syntax-highlighting,danielshahaf/zsh-syntax-highlighting-debian,stuha/wbr-zsh,m0vie/zsh-syntax-highlighting,zsh-users/zsh-syntax-highlighting,danielshahaf/zsh-syntax-highlighting,danielshahaf/zsh-syntax-highlighting,P71/zsh-syntax-highlighting,phy1729/zsh-syntax-highlighting,x-way/zsh-syntax-highlighting,phy1729/zsh-syntax-highlighting,joshuarubin/dotfiles,psprint/zsh-syntax-highlighting,m0vie/zsh-syntax-highlighting,P71/zsh-syntax-highlighting