Merge pull request cocoabits#38 from philippb/patch-1

Adding explanation for Swift usage

README.md

@@ -4,4 +4,9 @@ This component is intended as a replacement for SS_PrefsController by Matt Legen
 
 # How to use
 
-You can find a Demo project at [MASPreferencesDemo](https://github.com/shpakovski/MASPreferencesDemo).
+You can find a Demo project at [MASPreferencesDemo](https://github.com/shpakovski/MASPreferencesDemo).
+
+##Swift Edge case
+When using Swift you need to override the `identifier` from `MASPreferencesViewController` the following to be compatible with the mutable identifier `String?` in `NSViewController`
+
+    override var identifier: String? { get {return "general"} set { super.identifier = newValue} }