Added Supported .NET framework

README.md

@@ -35,6 +35,10 @@ PM> Install-Package WebSocketSharp -Pre
 
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+## Supported .NET framework ##
+
+**websocket-sharp** supports .NET **3.5** compatible or later.
+
 ## Usage ##
 
 ### WebSocket Client ###
@@ -426,10 +430,6 @@ ws.Log.Debug ("This is a debug message.");
 
 The `WebSocketServer` and `HttpServer` classes include the same logging functions.
 
-## Required Environment ##
-
-C# **3.0**, .NET **3.5** compatible or later.
-
 ## Examples ##
 
 Examples using **websocket-sharp**.