Add Carthage install instructions

Author: perryprog

README.md

@@ -9,10 +9,16 @@ An extension to make serializing [Alamofire](https://github.com/Alamofire/Alamof
 
 ## Install
 
+CocoaPods:
 ```ruby
 pod 'Alamofire-SwiftyJSON'
 ```
 
+Carthage:
+```
+github "SwiftyJSON/Alamofire-SwiftyJSON" "master"
+```
+
 ## Usage
 
 ```swift