Update README with separate vector database example

[mhaugel]

Hi! Thanks for a great project!

Would it be possible to add an example to the README of how to use a separate vector database?

Thanks!

[nandhaece07]

@mhaugel is this resolved? I am also looking for the external vector db integration example.

[jamesbraza]

This is roughly documented in https://github.com/Future-House/paper-qa/tree/v5.0.0?tab=readme-ov-file#using-external-dbvector-db-and-caching. It can definitely use more information, we are open to docs contributions