Add requirement.txt for easier installation of packages

[lyqht]

Hey there! I came from dev.to and read your article on using langchain & streamlit to chat with csv!

I saw a comment on your article that someone missed out an installation step, so I was thinking it might be better to have a requirements.txt to install the packages more easily. Have updated the readme with that step too.

[Ngonie-x]

Thanks for the contribution! Really appreciated.