How to Build HTML

1. Update the .rst file in docs_using_sphinx
2. Run terminal, changing work directory to docs_using_sphinx
3. run python3 -m venv .env for the virtual environment
4. run source .env/bin/activate to activate
5. run pip install -r requirements.txt to install dependencies
6. Run make html. The updated pages locate in ./_build/html
7. Copy all the files under ./_build/html to repository easy-graph.github.io
8. Push the changes to origin masters of these two repository