Update README.md

Update cocoapod install to be compatible with cocoapod 1.x as it now requires a concrete target.

README.md

@@ -70,7 +70,9 @@ source 'https://github.com/CocoaPods/Specs.git'
 platform :ios, '9.0'
 use_frameworks!
 
-pod 'Alamofire', '~> 3.4'
+target '<Your Target Name>' do
+    pod 'Alamofire', '~> 3.4'
+end
 ```
 
 Then, run the following command: