Adding github settings.yml

This lets us centrally define access permissions to our repositories
and other sensible defaults where approrpriate. You can see the
defaults in the [github-apps-config-next][defaults] repo. For full
configuration options check out the [probot settings repo][probot].

[defaults]: https://github.com/Financial-Times/github-apps-config-next/blob/master/.github/settings.yml
[probot]: https://github.com/probot/settings

.github/settings.yml

@@ -0,0 +1 @@
+_extends: github-apps-config-next