Missing CodingGuidelines

[hickford]

Please publish https://github.com/git/git/blob/master/Documentation/CodingGuidelines (format unclear) to https://git-scm.com/docs/CodingGuidelines

[dscho]

Just as with ReviewingGuidelines, I am opposed to including documentation that is specific to the Git project.

[dscho]

→ #1965