Added index.md

Added index.md with explanation which seems a little bit short of detail.
Fixed the directory of the files.

value-object/src/main/java/com/iluwatar/value/object/App.java

@@ -0,0 +1,12 @@
+package com.iluwatar.value.object;
+
+/**
+ * Hello world!.
+ *
+ */
+public class App {
+  public static void main(String[] args) {
+    HeroStat stat = HeroStat.valueOf(10, 5, 0);
+    System.out.println(stat.toString());
+  }
+}