Rename helloworld.rb to helloworld.cpp

.github/helloworld.cpp

@@ -0,0 +1,16 @@
+// A Hello World! program in C#.
+using System;
+namespace HelloWorld
+{
+    class Hello 
+    {
+        static void Main() 
+        {
+            Console.WriteLine("Hello World");
+
+            // Keep the console window open in debug mode.
+            Console.WriteLine("Press any key to exit.");
+            Console.ReadKey();
+        }
+    }
+}