Add comment README sample

README.md

@@ -284,6 +284,7 @@ let keychain = Keychain(service: "com.example.github-token")
 
 dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {
     do {
+        // Should be the secret invalidated when passcode is removed? If not then use `.WhenUnlocked`
         try keychain
             .accessibility(.WhenPasscodeSetThisDeviceOnly, authenticationPolicy: .UserPresence)
             .set("01234567-89ab-cdef-0123-456789abcdef", key: "kishikawakatsumi")
@@ -308,6 +309,7 @@ let keychain = Keychain(service: "com.example.github-token")
 
 dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {
     do {
+        // Should be the secret invalidated when passcode is removed? If not then use `.WhenUnlocked`
         try keychain
             .accessibility(.WhenPasscodeSetThisDeviceOnly, authenticationPolicy: .UserPresence)
             .authenticationPrompt("Authenticate to update your access token")