Replace broken readme image with new communicating instructions.

Author: timbotimbo

README.md

@@ -564,25 +564,57 @@ If you computer does not have an ARM processor, like most computers running on I
 
 ## Communicating 
 
-### Flutter-Unity
+### Flutter -> Unity
 
 1. On a `UnityWidget` widget, get the `UnityWidgetController` received by the `onUnityCreated` callback.
 
+```dart
+// Assign such a function to onUnityCreated of UnityWidget.
+void _onUnityCreated(UnityWidgetController controller) {
+  _unityWidgetController = controller;
+}
+```
+
 2. Use the method `postMessage` to send a string, using the GameObject name and the name of a behaviour method that should be called.
 
-### Unity-Flutter
 
-1. Select the GameObject that should execute the communication and go to **Inspector > Add Component > Unity Message Manager**.
+```dart
+// Snippet of postMessage usage in the example project.
+_unityWidgetController?.postMessage(
+  'Cube', // GameObject name
+  'SetRotationSpeed', // function in attached C# script
+  speed, // Function parameter (string)
+);
+```
 
-<img src="https://i.stack.imgur.com/1gSOy.png" width="400" />
+### Unity -> Flutter
 
-2. Create a new `MonoBehaviour` subclass and add to the same GameObject as a script.
+1. Add a `UnityMessageManager` component to you scene.
+    - Either click `Add Component` -> `UnityMessageManager` on a GameObject in you scene.
+    - Or call AddComponent in a MonoBehaviour script.
+    `gameObject.AddComponent<UnityMessageManager>();`
 
-3. On this new behaviour, call `GetComponent<UnityMessageManager>()` to get a `UnityMessageManager`.
+2. `UnityMessageManager` only needs to be added once. It is a Singleton which can be called from any other script in the scene.  Just use `UnityMessageManager.Instance`.
 
-4. Use the method `SendMessageToFlutter` to send a string. Receive this message using the `onUnityMessage` callback of a `UnityWidget`.
 
+3. Use the method `SendMessageToFlutter` to send a string. Receive this message using the `onUnityMessage` callback of a `UnityWidget`.
 
+```C#
+// Send a basic string to Flutter
+UnityMessageManager.Instance.SendMessageToFlutter("Hello there!");
+```
+4. If you want to send multiple parameters or objects, you will have to use a JSON string.
+```C#
+// This is a random object serialized to JSON using Json.net.
+JObject o = JObject.FromObject(new
+{
+    id = 1,
+    name = "Object 1",
+    whatever = 12
+});
+UnityMessageManager.Instance.SendMessageToFlutter(o.ToString());
+// You will need to deserialize this in Flutter after receiving it in OnUnityMessage.
+```
 
 
 ## Examples