CON-2557-Markdown-Reverse-Array-exercise (#2527)

* docs: adding subject

* docs: rephrase exercice description to improve its clarity

---------

Co-authored-by: amine <aaitihia@leyton.com>

subjects/java/checkpoints/reverse-array/README.md

@@ -0,0 +1,39 @@
+## ReverseArray
+
+### Instructions
+
+Create a Java file named `ReverseArray.java` and define a function named `reverse` inside it. This function should take an array as input, reverse the order of its elements, and return the new reversed array.
+
+### Expected Functions
+
+```java
+public class ReverseArray {
+    public static Integer[] reverse(Integer[] arr) {
+        // your code here
+    }
+}
+```
+
+### Usage
+
+Here is a possible `ExerciseRunner.java` to test your function :
+
+```java
+import java.io.*;
+import java.util.Arrays;
+
+public class ExerciseRunner {
+    public static void main(String[] args) throws IOException {
+        System.out.println(Arrays.toString(ReverseArray.reverse(new Integer[]{4, 2, 1, 3})));
+    }
+}
+```
+
+and its output :
+
+```shell
+$ javac *.java -d build
+$ java -cp build ExerciseRunner
+[3, 1, 2, 4]
+$
+```