add csharp examples (#10)

03_recursion/csharp/02_greet/Program.cs

@@ -0,0 +1,30 @@
+using System;
+
+namespace ConsoleApplication
+{
+    public class Program
+    {
+        public static void Main(string[] args)
+        {
+            Greet("adit");
+        }
+
+        private static void Greet(string name)
+        {
+            Console.WriteLine($"hello, {name}!");
+            Greet2(name);
+            Console.WriteLine("getting ready to say bye...");
+            Bye();
+        }
+
+        private static void Greet2(string name)
+        {
+            Console.WriteLine($"how are you, {name}?");
+        }
+
+        private static void Bye()
+        {
+            Console.WriteLine("ok bye!");
+        }
+    }
+}