Added minimal example csharp (C#) visual studio project

examples/csharp_vsproj_dll/libztHelloWorld_csharp/Program.cs

@@ -0,0 +1,24 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+using ZeroTier;
+
+namespace libztHelloWorld_csharp
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            Console.Write("waiting for libzt to come online...\n");
+            libzt.zts_startjoin("config_path", "17d709436c2c5367");
+            Console.Write("started. now performing a socket call\n");
+            int fd = libzt.zts_socket(2, 1, 0);
+            Console.Write("fd=%d\n", fd);
+            // zts_connect(), zts_bind(), etc...
+            libzt.zts_stop();
+        }
+    }
+}