Merge pull request #372 from ntumlgroup/update_readme

Update doc readme

Author: Eleven1Liu

docs/readme

@@ -1,5 +1,6 @@
 To build the documentation, please set up Python 3.8 and:
     pip install -r ../requirements.txt
+    pip install -r ../requirements_nn.txt
     pip install -r requirements.txt
     git submodule init
     git submodule update