Update TopFuture.md

Author: SoftStoneDevelop

Documentation/Stack/TopFuture.md

@@ -19,3 +19,21 @@ Exception
 ```
 
 If Future element not available
+
+```C#
+
+unsafe
+{
+    using (var memory = new StackMemoryCollections.Struct.StackMemory(sizeof(int) * 10))
+    {
+        using var stack = new StackMemoryCollections.Struct.StackOfInt32(10, &memory);
+        for (int i = 0; i < 10; i++)
+        {
+            int* futureTop = stack.TopFuture();
+            *futureTop = i;
+            stack.PushFuture();
+        }
+    }
+}
+
+```