docs: Update recommended installation method(s)

Author: kylef

README.md

@@ -6,12 +6,14 @@ Swift implementation of [JSON Web Token](https://tools.ietf.org/html/draft-ietf-
 
 ## Installation
 
-[CocoaPods](http://cocoapods.org/) is the recommended installation method.
+Swift Pacakage Manager is the recommended installation method for JSONWebToken, [CocoaPods](http://cocoapods.org/) is also supported.
 
 ```ruby
 pod 'JSONWebToken'
 ```
 
+**NOTE:** *Carthage may be supported, however support will not be provided for this installation method, use at your own risk if you know how it works.*
+
 ## Usage
 
 ```swift