docs(readme): add Greenkeeper badge

greenkeeper[bot] · greenkeeper[bot] · commit d20fc4753923 · 2017-04-22T20:27:23.000Z
diff --git a/README.md b/README.md
@@ -1,4 +1,6 @@
 # 🍭 CSS in React
+
+[![Greenkeeper badge](https://badges.greenkeeper.io/joeshub/css-in-react.svg)](https://greenkeeper.io/)
 Learn the best frameworks by example
 
 ## Cheat Sheet
