update README.md

Author: int32bit

README.md

@@ -113,6 +113,7 @@
 + [205 Isomorphic Strings](algorithms/IsomorphicStrings)
 + [206 Reverse Linked List(链表转置，递归&迭代)](algorithms/ReverseLinkedList)
 + [208 Implement Trie (Trie树、字典树、前缀树)](algorithms/ImplementTrie)
++ [211 Add and Search Word - Data structure design(Trie树)](algorithms/AddandSearchWord)
 
 ## Database