Update README.md

Author: krystism

algorithms/MergekSortedLists/README.md

@@ -128,3 +128,10 @@ ListNode *mergeKLists_withMerge(vector<ListNode *> &lists, int s, int t)
 		return mergeTwoList(left, right);
 	}
 ```
+
+## 扩展
+
+* [Merge Two Sorted Lists](../MergeTwoSortedLists): 合并两个链表
+* [Merge k Sorted Lists](../MergekSortedLists): 合并K个链表
+* [Merge Sorted Array](../MergeSortedArray): 合并两个数组
+* [Sort List](../SortList): 归并排序两个链表