feat(third_party): Check in git-appraise

third_party/go/git-appraise/CONTRIBUTING.md

@@ -0,0 +1,24 @@
+Want to contribute? Great! First, read this page (including the small print at the end).
+
+### Before you contribute
+Before we can use your code, you must sign the
+[Google Individual Contributor License Agreement](https://developers.google.com/open-source/cla/individual?csw=1)
+(CLA), which you can do online. The CLA is necessary mainly because you own the
+copyright to your changes, even after your contribution becomes part of our
+codebase.  Therefore, we need your permission to use and distribute your code.
+We also need to be sure of various other things—for instance that you'll tell
+us if you know that your code infringes on other people's patents. You don't
+have to sign the CLA until after you've submitted your code for review and a
+member has approved it, but you must do it before we can put your code into our
+codebase. Before you start working on a larger contribution, you should get in
+touch with us first through the issue tracker with your idea so that we can
+help out and possibly guide you. Coordinating up front avoids frustrations later.
+
+### Code reviews
+All submissions, including submissions by project members, require review. You
+may use a Github pull request to start such a review, but the review itself
+will be conducted using this tool.
+
+### The small print
+Contributions made by corporations are covered by a different agreement than
+the one above, the Software Grant and Corporate Contributor License Agreement.