New feature of 4.0 (#175)

* New feature of 4.0

* Reference 4.0 in the version guidance note

* 3 -> 4

Author: bobiechen-twilio

Docs/new-features-4.0.md

@@ -0,0 +1,23 @@
+## SDK 4.0 New Features
+Voice iOS SDK 4.0 introduced a new call state: `TVOCallStateReconnecting`. You will need to update any logic you have implemented that relies on the call state. The simplest approach is to treat a `TVOCallStateReconnecting` just like a `TVOCallStateConnected` and keep the current behavior.
+
+For more advanced behaviour, you can make use of TVOCallDelegate’s new protocol methods `call:isReconnectingWithError:` and `callDidReconnect:` to update the UI for example and indicate the ongoing disruption.
+
+For example:
+
+```
+- (void)call:(TVOCall *)call isReconnectingWithError:(NSError *)error {
+    NSLog(@"Call is reconnecting");
+
+    // Update UI
+    // Check the error: It could be either
+    // TVOErrorSignalingConnectionDisconnectedError (53001) or
+    // TVOErrorMediaConnectionError (53405).
+}
+
+- (void)callDidReconnect:(TVOCall *)call {
+    NSLog(@"Call reconnected");
+
+    // Update UI
+}
+```

README.md

@@ -1,10 +1,11 @@
 # Twilio Voice Objective-C Quickstart for iOS
 
-> NOTE: These sample applications use the Twilio Voice 3.x APIs. For examples using our 2.x APIs, please see the [2.x](https://github.com/twilio/voice-quickstart-objc/tree/2.x) branch. If you are using SDK 2.x, we highly recommend planning your migration to 3.0 as soon as possible. Support for 2.x will cease 1/1/2020. Until then, SDK 2.x will only receive fixes for critical or security related issues.
+> NOTE: These sample applications use the Twilio Voice 4.x APIs. For examples using our 2.x APIs, please see the [2.x](https://github.com/twilio/voice-quickstart-objc/tree/2.x) branch. If you are using SDK 2.x, we highly recommend planning your migration to 4.0 as soon as possible. Support for 2.x will cease 1/1/2020. Until then, SDK 2.x will only receive fixes for critical or security related issues.
 
 ## Get started with Voice on iOS:
 * [Quickstart](#quickstart) - Run the quickstart app
-* [New Features](Docs/new-features-3.0.md) - New features in 3.0
+* [4.0 New Features](Docs/new-features-4.0.md) - New features in 4.0
+* [3.0 New Features](Docs/new-features-3.0.md) - New features in 3.0
 * [Migration Guide](Docs/migration-guide-2.x-3.x.md) - Migrating from 2.X to 3.x
 * [Access Tokens](#access-tokens) - Using access tokens
 * [Managing Audio Interruptions](#managing-audio-interruptions) - Managing audio interruptions