Issue 2100: Explanation of branches for CG (issue 5539062)

[Carl . D . Sorensen]

Reviewers: Graham Percival, Keith, janek,

Message:
Here's a revision of Graham's info for the CG on branches.  I think it
can go in as-is.

Please review.

Thanks,

Carl


Description:
Issue 2100: Explanation of branches for CG

Explain branches, by Graham Percival
Changes to git commands by Carl Sorensen

Please review this at http://codereview.appspot.com/5539062/

Affected files:
  M Documentation/contributor/source-code.itexi