Documentation misses the setup of the enviroment variables for the model

[tobiasgrossmann]

Lack of documentation on how to set up the environmental variables for the model.

cap-llm-plugin.js will fail:

`
   const EMBEDDING_MODEL_DESTINATION_NAME = cds.env.requires?.["GENERATIVE_AI_HUB"]?.["EMBEDDING_MODEL_DESTINATION_NAME"];
      const EMBEDDING_MODEL_DEPLOYMENT_URL = cds.env.requires?.["GENERATIVE_AI_HUB"]?.["EMBEDDING_MODEL_DEPLOYMENT_URL"];
      const EMBEDDING_MODEL_RESOURCE_GROUP = cds.env.requires?.["GENERATIVE_AI_HUB"]?.["EMBEDDING_MODEL_RESOURCE_GROUP"];
      const EMBEDDING_MODEL_API_VERSION = cds.env.requires?.["GENERATIVE_AI_HUB"]?.["EMBEDDING_MODEL_API_VERSION"];
`