Add a note to the README about customization.
Add a note to the README about customization.

ianyh/Amethyst,egabancho/Amethyst,cevaris/Amethyst,ianyh/Amethyst,olsonpm/Amethyst,egabancho/Amethyst,ianyh/Amethyst,olsonpm/Amethyst,cevaris/Amethyst,m4rw3r/Amethyst,hooplaaa/Amethyst,hooplaaa/Amethyst,m4rw3r/Amethyst,ianyh/Amethyst,ianyh/Amethyst