docs(readme): add Greenkeeper badge

greenkeeper[bot] · greenkeeper[bot] · commit 334c88e22e49 · 2017-01-20T21:48:41.000Z
https://greenkeeper.io/
diff --git a/README.md b/README.md
@@ -1,5 +1,7 @@
 # ANSI to React
 
+[![Greenkeeper badge](https://badges.greenkeeper.io/nteract/ansi-to-react.svg)](https://greenkeeper.io/)
+
 Convert ANSI Escape Codes to pretty text output for React.
 
 ```
