Updates to using Airflow with dbt. (#651)

Author: crericha

docs/integrations/dbt.md

@@ -82,13 +82,29 @@ Add SQLMesh [unit tests](../concepts/tests.md) to a dbt project by placing them
 ## Using Airflow
 To use SQLMesh and dbt projects with Airflow, first configure SQLMesh to use Airflow as described in the [Airflow integrations documentation](./airflow.md).
 
-Then, add the following to `config.py` within the project root directory:
+Then, install dbt-core within airflow.
+
+Finally, replace the contents of `config.py` with:
 
 ```bash
-> airflow_config = sqlmesh_config(Path(__file__).parent, scheduler=AirflowSchedulerConfig())
+> from pathlib import Path
+>
+> from sqlmesh.core.config import AirflowSchedulerConfig
+> from sqlmesh.dbt.loader import sqlmesh_config
+>
+> config = sqlmesh_config(
+>     Path(__file__).parent, 
+>     scheduler=AirflowSchedulerConfig(
+>         airflow_url="https://<Airflow Webserver Host>:<Airflow Webserver Port>/",
+>         username="<Airflow Username>",
+>         password="<Airflow Password>",
+>     )
+> )
 ```
 
-See the [Airflow configuration documentation](https://airflow.apache.org/docs/apache-airflow/2.1.0/configurations-ref.html) for a list of all AirflowSchedulerConfig configuration options.
+See the [Airflow configuration documentation](https://airflow.apache.org/docs/apache-airflow/2.1.0/configurations-ref.html) for a list of all AirflowSchedulerConfig configuration options. Note: only the python config file format is supported for dbt at this time.
+
+The project is now configured to use airflow. Going forward, this also means that the engine configured in airflow will be used instead of the target engine specified in profiles.yml.
 
 ## Supported dbt jinja methods