Updated README.md

Author: lokeshgupta1981

src/main/java/com/howtodoinjava/core/collections/map/README.md

@@ -2,4 +2,5 @@
 
 * [Merge Two Maps](https://howtodoinjava.com/java/collections/hashmap/merge-two-hashmaps/)
 * [Java WeakHashMap](https://howtodoinjava.com/java/collections/java-weakhashmap/)
-* [Java IdentityHashMap](https://howtodoinjava.com/java/collections/java-identityhashmap/)
+* [Java IdentityHashMap](https://howtodoinjava.com/java/collections/java-identityhashmap/)
+* [Java Nested Map](https://howtodoinjava.com/java/collections/java-nested-map/)