added custom color filename in README
added custom color filename in README

nextras/blog-theme,davidtorcivia/Steam,paulwellnerbou/Steam,ChiMarvine/Steam,paulwellnerbou/Steam,epistrephein/Steam,nextras/blog-theme,prakhar625/Steam,epistrephein/Steam,ruddra/Steam,kdelfour/ghost-steam-theme,ruddra/Steam