Update readme with Swift 4 branch info.

readme.md

@@ -8,22 +8,18 @@ Handle is an easy-to-use, expressive Swift library for handling notifications.
 
 ### 1. Update your Cartfile
 
-**Swift 3 (latest version)**
+**Swift 3 (master branch)**
 
-```
-git "git@source.ind.ie:project/handle.git" ~> 4.0
-```
-
-For Swift 2.3:
+(As of version 5.0, Handle is safe to use in App Extensions.)
 
 ```
-git "git@source.ind.ie:project/handle.git" "swift-2.3"
+git "git@source.ind.ie:project/handle.git" ~> 5.0
 ```
 
-To stay on Swift 2.2:
+For Swift 4 (Xcode 9 Beta):
 
 ```
-git "git@source.ind.ie:project/handle.git" ~> 3.0.1
+git "git@source.ind.ie:project/handle.git" "swift-4"
 ```
 
 ### 2. Add the framework to your Xcode project