Document what the endpoint should be set to

Right now you have to guess what the endpoint value should be - it might be useful to provide a selector?

After I connected the correct API key face🤦‍♂️ it still doesn't work and gives this error instead:

Could not load the embeddings engine to get the dimensions. Please check the configuration.Client error: `POST https://api-inference.huggingface.co/models/intfloat/e5-mistral-7b-instruct` resulted in a `404 Not Found` response: Not Found

The 404 error is related to a HF problem: https://discuss.huggingface.co/t/persistent-404-not-found-errors-with-pu...