Git introduction

src:
- http://git-scm.com/book/en/v2/Getting-Started-Git-Basics
  https://docs.google.com/file/d/0B543p5wfySTQY2l2c3JDbkw5U3M/edit (mypdf)


notes:
15'2/26:
- Git use snapshot instead of file backup
- offline support
- 3 states : committed, modified, staged (loops)
- [TODO] check the operation & setup