Update subscriber.md

tutorials/ros_unity_integration/subscriber.md

 
 ![](images/tcp_2.gif)
 
+## ROSSubscriberExample script
+
+```csharp
+using UnityEngine;
+using Unity.Robotics.ROSTCPConnector;
+using RosColor = RosMessageTypes.RoboticsDemo.MUnityColor;
+
+public class RosSubscriberExample : MonoBehaviour
+{
+    public GameObject cube;
+
+    void Start()
+    {
+        ROSConnection.instance.Subscribe<RosColor>("color", ColorChange);
+    }
+
+    void ColorChange(RosColor colorMessage)
+    {
+        cube.GetComponent<Renderer>().material.color = new Color32((byte)colorMessage.r, (byte)colorMessage.g, (byte)colorMessage.b, (byte)colorMessage.a);
+    }
+}
+```
+
+### Import Statements for Subscriber and Messages 
+
+```csharp
+using UnityEngine;
+using Unity.Robotics.ROSTCPConnector;
+using RosColor = RosMessageTypes.RoboticsDemo.MUnityColor;
+```
+
+### Instantiating the ROS Subscriber in unity
+
+```csharp
+void Start()
+    {
+        ROSConnection.instance.Subscribe<RosColor>("color", ColorChange);
+    }
+```
+We declare the topic to be subscribed before the program execution starts. This is done in the `Start()` function of the MonoBehavior. We add the topic we want to subscribe to the internal dictionary of our ROSConnection instance using `Subscribe` API.
+
+### Subscribe API
+```csharp
+public void Subscribe<T>(string topic, Action<T> callback)
+```
+### Summary
+Its a non-static member of ROSConnection class. It is used to add a ROS subscriber to the internal ROSConnection Dictionary.
+### Type Parameter
+T: ROS message type published in the topic to be subscribed.
+### Parameters
+ Parameters  | Description |
+| ------------- | ------------- |
+| `string topic`  | Name of the topic to be subscribed on the ROS machine  |
+| `Action<T> callback`  | Callback function used to process the received message |
+
+### Implementing the callback function
+
+```csharp
+void ColorChange(RosColor colorMessage)
+    {
+        cube.GetComponent<Renderer>().material.color = new Color32((byte)colorMessage.r, (byte)colorMessage.g, (byte)colorMessage.b, (byte)colorMessage.a);
+    }
+```
+
+After a message is received in Unity, a callback function is called to process the incoming message. The callback is a delegate which defines a function that receives one parameter and returns nothing as described [here](https://docs.microsoft.com/en-us/dotnet/api/system.action-1?view=net-5.0). In this Subscribe API, that parameter is the message published in the topic. 
+In this example we extract the color's attributes from the message and assign it to the cube's material.
+
+> Please reference [networking troubleshooting](network.md) doc if any errors are thrown.
+
+![](images/tcp_2.gif)
+
+
 Continue to the [ROS–Unity Integration Service](service.md).