improve docs
improve docs

blipjoy/chessboardjs,mattyhead/chessboardjs,ngocdaothanh/chessboardjs,blipjoy/chessboardjs,mauronunez/chessboardjs,ngocdaothanh/chessboardjs,blipjoy/chessboardjs,raneku/chessboardjs,oakmac/chessboardjs,raneku/chessboardjs,ThiagoGarciaAlves/chessboardjs,mattyhead/chessboardjs,raneku/chessboardjs,ThiagoGarciaAlves/chessboardjs,mauronunez/chessboardjs