Add git clients page
Change "programmers" term by "hackers"

Also, change "git" by "Git"
Add pros and cons to "command line tool"
Complete "Git Extensions" section
Minor fix in Git command line tools pros and cons title
Add "GitHub for Windows" pros and cons
Move "Git Extensions" upper

(because it is my favorite)
Move "Git Clients" page inside "Working with Git" area.
Minor changes on content organization
Minor titles layout changes
Add some content to Working with Git area
Fix some typos
Merge pull request #2 from andresmoschini/add-content

Changes