Update MLFlow saving method

Updating the MLFlow saving method including tracking uri.

docs/userguide/torch_forecasting_models.md

@@ -500,7 +500,7 @@ mlflow.pytorch.autolog(log_every_n_epoch=1, log_every_n_step=None,
 import mlflow.pytorch
 from mlflow.client import MlflowClient
 
-model_name = "Darts"
+model_name = "darts-NBEATS"
 
 with mlflow.start_run(nested=True) as run:
 
@@ -545,14 +545,13 @@ mlflow.pytorch.get_default_conda_env()
 mlflow.pytorch.get_default_pip_requirements()
 
 # Set tracking uri
-mlflow.set_tracking_uri("sqlite:///mlruns.db")
+model_uri = f"runs:/{run.info.run_id}/darts-NBEATS"
 
-# Save Darts model (this need to be added via new cell)
-mlflow.log_artifact("NBeatsModel.pickle")
+# Save Darts model as an artifact
+model_path = 'nbeats_air_passengers'
+mlflow.sklearn.save_model(model, model_path)
 
 # Registering model
-model_name = "NBEATS"
-model_uri = f"runs:/{run.info.run_id}/darts-NBEATS"
 mlflow.register_model(model_uri=model_uri, name=model_name)
 ```