Merge branch 'jk/promote-ggg'

Suggest GitGitGadget instead of submitGit as a way to submit
patches based on GitHub PR to us.

* jk/promote-ggg:
  point pull requesters to GitGitGadget

.github/CONTRIBUTING.md

@@ -5,7 +5,7 @@ Git community does not use github.com for their contributions. Instead, we use
 a mailing list (git@vger.kernel.org) for code submissions, code
 reviews, and bug reports.
 
-Nevertheless, you can use [submitGit](http://submitgit.herokuapp.com/) to
+Nevertheless, you can use [GitGitGadget](https://gitgitgadget.github.io/) to
 conveniently send your Pull Requests commits to our mailing list.
 
 Please read ["A note from the maintainer"](https://git.kernel.org/pub/scm/git/git.git/plain/MaintNotes?h=todo)

.github/PULL_REQUEST_TEMPLATE.md

 Thanks for taking the time to contribute to Git! Please be advised that the
 Git community does not use github.com for their contributions. Instead, we use
 a mailing list (git@vger.kernel.org) for code submissions, code reviews, and
-bug reports. Nevertheless, you can use submitGit to conveniently send your Pull
-Requests commits to our mailing list.
+bug reports. Nevertheless, you can use GitGitGadget (https://gitgitgadget.github.io/)
+to conveniently send your Pull Requests commits to our mailing list.
 
 Please read the "guidelines for contributing" linked above!