Add Setup Instructions for Azure OpenAI

Hi there,

It took me a while to get Cannoli to work with Azure OpenAI because of a tiny detail with the way I configured the endpoint.
**I'd like to suggest adding instructions to let users know that:**

1. The "Azure base url" field is actually optional
2. Is the user wants to use a particular endpoint, it should follow the format https://[your-instance-name].openai.azure.com/openai/deployments

Also, it would probably also be useful to explain in the docs or help menus that "instance-name" is equivalent to the resource name.

Cheers!