[README] Remove mention of Swift Package Manager

Author: kylef

README.md

@@ -12,20 +12,6 @@ Swift implementation of [JSON Web Token](https://tools.ietf.org/html/draft-ietf-
 pod 'JSONWebToken'
 ```
 
-[Swift Package Manager](https://swift.org/package-manager/) installation is also available with the following dependency:
-
-```swift
-import PackageDescription
-
-let package = Package(
-  name: "AwesomeProject",
-  dependencies: [
-    .Package(url: "https://github.com/kylef/JSONWebToken.swift", versions: Version(1,4,2)..<Version(1,5,0))
-  ]
-)
-
-```
-
 ## Usage
 
 ```swift