add gitignore
Merge branch 'master' of https://github.com/niying126/CS2114
Merge branch 'master' of https://github.com/niying126/CS2114
Merge branch 'master' of https://github.com/niying126/CS2114
Merge branch 'master' of https://github.com/niying126/CS2114
add example for Ying