README: Expand the at-end-of-.zshrc FAQ answer.
README: Expand the at-end-of-.zshrc FAQ answer.

Fixes zsh-users/zsh-syntax-highlighting#185.

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