Jupyter Notebook 注释的时候保持缩进

https://github.com/jupyter/notebook/issues/954

用Ctrl+/给Jupyter Notebook注释的时候，注释出现在行首显得代码有点乱。我在上面的链接找到了一个方法。

conda update notebook 
conda install jupyter notebook 
conda install -c conda-forge jupyter_nbextensions_configurator 
conda install -c conda-forge jupyter_contrib_nbextensions

pip install jupyter_contrib_nbextensions
jupyter contrib nbextension install --user
jupyter nbextension enable comment-uncomment/main

# This program prints Hello, world! 
print('Hello, world!')