Move Program.cs and convert to Program.main

Program.cs

@@ -1,2 +0,0 @@
-// See https://aka.ms/new-console-template for more information
-Console.WriteLine("Hello, World!");

src/Program.cs

@@ -0,0 +1,7 @@
+internal class Program
+{
+  private static void Main(string[] args)
+  {
+    Console.WriteLine("Hello, World!");
+  }
+}