Update README.md

Author: jpotts18

README.md

@@ -1,7 +1,7 @@
 SwiftValidator
 ===============
 
-[![Build Status](https://travis-ci.org/jpotts18/SwiftValidator.svg?branch=travis-ci)](https://travis-ci.org/jpotts18/SwiftValidator)
+[![Build Status](https://travis-ci.org/jpotts18/SwiftValidator.svg?branch=travis-ci)](https://travis-ci.org/jpotts18/SwiftValidator) [![Carthage compatible](https://img.shields.io/badge/Carthage-compatible-4BC51D.svg?style=flat)](https://github.com/Carthage/Carthage)
 
 Swift Validator is a rule-based validation library for Swift.