docs(readme): add Greenkeeper badge

greenkeeper[bot] · greenkeeper[bot] · commit 1b8735ad98a8 · 2018-01-18T20:34:47.000Z
diff --git a/README.md b/README.md
@@ -1,5 +1,7 @@
 # [WIP] optimizing-css-compiler
 
+[![Greenkeeper badge](https://badges.greenkeeper.io/html-next/optimizing-css-compiler.svg)](https://greenkeeper.io/)
+
 What does a little convention get you? A lot, as it turns out.
 
 When following the conventions listed below, the Optimizing CSS Compiler
