Update README.md

README.md

@@ -23,6 +23,7 @@ Task: Summarization
 ## Usage
 ```python
 from transformers import PegasusForConditionalGeneration,BertTokenizer
+from typing import List, Optional
 import jieba
 jieba.initialize()
 # Need to download tokenizers_pegasus.py and other Python script from Fengshenbang-LM github repo in advance,