docs(readme): add Greenkeeper badge

greenkeeper[bot] · greenkeeper[bot] · commit 9ff576ed7d1d · 2018-04-10T21:49:53.000Z
diff --git a/README.md b/README.md
@@ -1,5 +1,7 @@
 # eslint-plugin-hbs
 
+[![Greenkeeper badge](https://badges.greenkeeper.io/psbanka/eslint-plugin-hbs.svg)](https://greenkeeper.io/)
+
 Provide linting for hbs template literals inside of JavaScript
 
 ## Installation
