Add description for SkipList.java (#3503)

Author: TanmayJadhav

src/main/java/com/thealgorithms/datastructures/lists/README.md

@@ -29,3 +29,4 @@ The `next` variable points to the next node in the data structure and value stor
 5. `DoublyLinkedList.java` : A modification of singly linked list which has a `prev` pointer to point to the previous node.
 6. `Merge_K_SortedLinkedlist.java` : Merges K sorted linked list with mergesort (mergesort is also the most efficient sorting algorithm for linked list).
 7. `RandomNode.java` : Selects a random node from given linked list and diplays it.
+8. `SkipList.java` : Data Structure used for storing a sorted list of elements with help of a Linked list hierarchy that connects to subsequences of elements.