Start writing tutorial.
Added a note file using strapdown.js.
Added Snapshots section.

* Added figures to describe differences between normal VCS, and Git
* Describe how Git tracks contents
* Additional link to see Git Object Model
Added a figure illustrating Git States.
Added walkthrough links.

* Link to Git Immersion tutorial
* Link to Interactive Git Branching
Added Git Configuration section.

* How to review config
* How to configure mergetool using kdiff3 or tortoise
* How to edit config file through text editor
Specified how the Walkthrough should be exercised.
Added a couple of commands to Basic section.

* add --interactive
* cherry-pick purpose
Added Branch topic.

* Illustrates branches as silos
* Illustrates topic branches and result after merged
Added Diff examples to the basic section.
Added branching topics.
Added difftool to the Diff section.