adds an example

Author: emad-elsaid

factorial_example_test.go

@@ -0,0 +1,19 @@
+package memoize
+
+import (
+	"fmt"
+)
+
+func ExampleFactorial() {
+	var factorial func(uint64) uint64
+	factorial = New(func(i uint64) uint64 {
+		if i == 0 {
+			return 1
+		}
+
+		return i * factorial(i-1)
+	})
+
+	fmt.Println(factorial(10))
+	// Output: 3628800
+}