Update README.md

Author: Husseinhj

README.md

@@ -1,2 +1,47 @@
 # NotificationCenter  [![Build Status](https://travis-ci.org/Husseinhj/NotificationCenter.svg?branch=master)](https://travis-ci.org/Husseinhj/NotificationCenter) ![Nuget version](https://img.shields.io/nuget/v/NotificationCenter.svg?style=flat) ![downloads](https://img.shields.io/nuget/dt/NotificationCenter.svg?style=flat)
 This library works like Objective-C and Swift NSNotificationCenter.
+
+## Installation 
+Use this command in Nuget Package Manager Console:
+
+``` ruby
+PM> Install-Package NotificationCenter -Version 1.0.0
+```
+
+## Methods
+### Subscribe
+To add an action with Key in NotificationCenter, You should use this code :
+
+``` csharp
+NotificationCenter.Subscribe("KEY",Action);
+
+private void Action()
+{
+    Debug.WriteLine("Action was run");
+}
+
+// or
+NotificationCenter.Subscribe("KEY",Action);
+
+private void Action(object o)
+{
+    Debug.WriteLine("Action was run with {0} object",o);
+}
+```
+
+### Unsubscribe
+To remove your action in NotificationCenter, You should use this code :
+
+``` csharp
+NotificationCenter.Unsubscribe("KEY");
+```
+
+### Notify
+To invoke or notify all actions in unique Key, You should use this code :
+
+``` csharp
+NotificationCenter.Notify(key: "KEY",data: 5);
+```
+
+### KeepActionValue property
+Keep action data if key was not subscribed yet. It just work in Notify with data.