Update README.md

update the answer for a question raised by developers.

README.md

@@ -138,6 +138,18 @@ $ python examples/tableqa/run_model.py predict --resource-dir ./tapex.large.wtq
 2021-08-29 17:39:47 | INFO | __main__ | The answer should be : 2004
 ```
 
+# ❓ Frequently Asked Questions
+
+### 1. AttributeError: 'NoneType' object has no attribute 'bpe'
+
+You should firstly check the version of fairseq, which should be `1.0.0a0+801a646` when you use `pip list` to show it.
+
+Note that the fairseq dependency is not officially released as `1.0.0`, so the one is not correct if you directly install it from `pip install fairseq`. Our installtion is equalivant to the following command:
+```shell
+pip install git+https://github.com/pytorch/fairseq.git@801a64683164680562c77b688d9ca77fc3e0cea7
+```
+It also requires you to have `Git` installed at first.
+
 
 # 💬 Citation