update README.md for Day012
update README.md for Day012

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