저자소개 오타 수정

- github 계정 주소를 변경(namsk -> seapy)
Gemfile의 작성에 Bundler 설치 섹션 추가

- Bundler 설치에 대한 코멘트가 없어 추가
Gemfile의 작성의 Bundler 설치 섹션 수정

- 젬 설치시 웹으로부터 다운로드 받는다는것을 추가
Merge pull request #12 from seapy/master

Bundler 설치 및 저자소개 수정