docs(readme): add Greenkeeper badge

greenkeeper[bot] · greenkeeper[bot] · commit ad060535a75d · 2017-08-13T09:44:12.000Z
diff --git a/README.md b/README.md
@@ -1 +1,3 @@
-# react-router-config-loader
+# react-router-config-loader
+
+[![Greenkeeper badge](https://badges.greenkeeper.io/grayyang/react-router-config-loader.svg)](https://greenkeeper.io/)
