Clarify in the README which models need to be deployed to use the AI chat feature

[danroth27]

I had to deploy specific models (gpt-35-turbo-16k, text-embedding-3-small) in my Azure OpenAI resource to get the text embeddings and chat functionality to work. I deduced this from reading through the code, but it seems like this should be called out explicitly in the README as part of the app setup instructions.