Include and output sources

[namuan]

Use VectorDBQAWithSourcesChain and return sources along with the answer.

Check if we can get page number so that an book page image can be displayed along with the answer?
Better if we can highlight the interesting sentences

[namuan]

Reference code:
https://github.com/hwchase17/notion-qa/blob/master/ingest.py
https://github.com/StevenVeshkini/ai_hackathon/blob/master/main.py
https://github.com/petehunt/langchain-github-bot/blob/main/langchain_bot_simple.py