Add a whatsdeployed.io badge to README

Author: notriddle

README.md

@@ -1,6 +1,7 @@
 # crates.io
 
 [![Build Status](https://travis-ci.org/rust-lang/crates.io.svg?branch=master)](https://travis-ci.org/rust-lang/crates.io)
+[![What's Deployed](https://img.shields.io/badge/whatsdeployed-prod-green.svg)](https://whatsdeployed.io/s-9IG)
 
 Source code for the default [Cargo](http://doc.crates.io) registry. Viewable
 online at [crates.io](https://crates.io).