Add configuration file for code review git integration.

This file allow the use of
   git cl upload    ; upload a code review (from a branch).
   git cl issue     ; see the code review id of a branch.
   git cl issue  XX ; set the code review id of a branch.

It is easier than using the upload script.

R=fw.centrale@gmail.com

BUG=

Review URL: https://codereview.appspot.com/12699044