docs(README): badges

Author: gr2m

README.md

@@ -2,6 +2,10 @@
 
 > GitHub API authentication library for browsers and Node.js
 
+[![@latest](https://img.shields.io/npm/v/@octokit/auth.svg)](https://www.npmjs.com/package/@octokit/auth)
+[![Build Status](https://travis-ci.com/octokit/auth.js.svg?branch=master)](https://travis-ci.com/octokit/auth.js)
+[![Greenkeeper](https://badges.greenkeeper.io/octokit/auth.js.svg)](https://greenkeeper.io/)
+
 GitHub supports 4 authentication strategies. They are all implemented in `@octokit/auth`.
 
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