Update OldCode.cs (#501)

Added a tag name around the full Student class, along with adding the property and constructor initialization of 'Grades'

Author: CalvinAllen

snippets/csharp/new-in-6/OldCode.cs

@@ -30,19 +30,23 @@ public string FullName
 
 namespace ReadOnlyOldStyle
 {
+    // <Student>
     public class Student
     {
         // <ClassicReadOnlyAutoProperty>
         public string FirstName { get; private set; }
         public string LastName { get; private set; }
+        public ICollection<double> Grades { get; private set; }
         // </ClassicReadOnlyAutoProperty>
 
         // <Construction>
         public Student(string firstName, string lastName)
         {
             FirstName = firstName;
             LastName = lastName;
+            Grades = new List<double>();
         }
         // </Construction>
     }
-}
+    // </Student>
+}