update README.md for Day004
update README.md for Day004

jacky-ttt/CodingEveryday,jacky-ttt/CodingEveryday,jacky-ttt/CodingEveryday,jacky-ttt/CodingEveryday,jacky-ttt/CodingEveryday,jacky-ttt/CodingEveryday,jacky-ttt/CodingEveryday,jacky-ttt/CodingEveryday