Add pizza implementation in c#

69_Pizza/csharp/Pizza/StringBuilderExtensions.cs

@@ -0,0 +1,21 @@
+using System.Text;
+
+namespace Pizza
+{
+    internal static class StringBuilderExtensions
+    {
+        /// <summary>
+        /// Extensions for adding new lines of specific value.
+        /// </summary>
+        /// <param name="stringBuilder">Extended class.</param>
+        /// <param name="value">Value which will be repeated.</param>
+        /// <param name="numberOfLines">Number of lines that will be appended.</param>
+        public static void AppendLine(this StringBuilder stringBuilder, string value, int numberOfLines)
+        {
+            for (int i = 0; i < numberOfLines; i++)
+            {
+                stringBuilder.AppendLine(value);
+            }
+        }
+    }
+}