Update map.md #158

Author: bowbahdoe

src/streams/map.md

@@ -13,6 +13,16 @@ Stream<Integer> numberStream = numbers.stream()
     .map(Integer::parseInt); // 1, 2, 3
 ```
 
+You can also call `.map` multiple times to apply multiple transformations.
+
+```java,no_run
+var numbers = List.of("1", "2", "3");
+
+Stream<Integer> numberStream = numbers.stream()
+    .map(Integer::parseInt)  // 1, 2, 3
+    .map(x -> x * 2); // 2, 4, 6
+```
+
 [^metaphor]: In the real life stream metaphor, this is akin to rocks getting polished
 by sand as they flow.