fix typo of README
fix typo of README

picrin-scheme/picrin,leavesbnw/picrin,koba-e964/picrin,ktakashi/picrin,leavesbnw/picrin,leavesbnw/picrin,koba-e964/picrin,ktakashi/picrin,picrin-scheme/picrin,koba-e964/picrin,ktakashi/picrin,dcurrie/picrin,omasanori/picrin,omasanori/picrin,dcurrie/picrin