Update README.MD (#58)

Author: stephentoub

README.MD

@@ -1,5 +1,7 @@
 # MCP C# SDK
 
+[![NuGet preview version](https://img.shields.io/nuget/vpre/ModelContextProtocol.svg)](https://www.nuget.org/packages/ModelContextProtocol/absoluteLatest)
+
 The official C# SDK for the [Model Context Protocol](https://modelcontextprotocol.io/), enabling .NET applications, services, and libraries to implement and interact with MCP clients and servers.
 
 > [!NOTE]