add doc

docs/getting_started/execution-modes.rst

@@ -92,6 +92,7 @@ Some drawbacks of this approach:
 
 - It is slower than ``local`` because it creates a new Python virtual environment for each Cosmos dbt task run.
 - If dbt is unavailable in the Airflow scheduler, the default ``LoadMode.DBT_LS`` will not work. In this scenario, users must use a `parsing method <parsing-methods.html>`_  that does not rely on dbt, such as ``LoadMode.MANIFEST``.
+- Only ``InvocationMode.SUBPROCESS`` is supported currently, attempt to use ``InvocationMode.DBT_RUNNER`` will raise error.
 
 Example of how to use: