Add README for lists (#2421)

DataStructures/Lists/README.md

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+## Linked List
+### Description
+
+LinkedList is a data structure in which data is stored in a linear manner. It usually contains a data field and a link to the memory location of the next mode.
+
+### Structure
+
+```
+class LinkedList<E>{
+    E value;
+    LinkedList next;
+}
+```
+
+The `next` variable points to the next node in the data structure and value stores the data. Any number of nodes can be linked in this manner. The structure will be:
+
+
+### Properties
+1. Linked list does not provide indexing like an array. For accessing a node at position `p` , &theta;(p) nodes need to be accessed.
+2. Main advantage of linked list is addition and removal of nodes near the end and beginning of lists. It can be done just by updating the link (O(1) time)
+3. Unlike an array, its size is not predefined. So any number of nodes can be appended.
+
+### File descriptions:
+
+1. `CircleLinkedList.java` : A circular linked list where next pointer of last node points to first nide of linked list.
+2. `SinglyLinkedList.java` : The classic case of single links.
+3. `CountSinglyLinkedListRecursion.java`: Recursively counts the size of a list.
+4. `detect_and_create_loop.java` : Detect a loop in linked list
+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).