docs(README): add npm badge

AndersDJohnson · web-flow · commit 1cfd14cdd3b2 · 2016-09-15T23:02:56.000-05:00
diff --git a/README.md b/README.md
@@ -1,5 +1,7 @@
 # conventional-commit-types
 
+[![npm](https://img.shields.io/npm/v/npm.svg?maxAge=2592000)](https://www.npmjs.com/package/conventional-commit-types)
+
 List of conventional commit types.
 
 ## Spec
