docs: Updated docstring of JdbcHook and mentioned importance of sqlal…

…chemy_scheme parameter

airflow/providers/jdbc/hooks/jdbc.py

@@ -62,7 +62,12 @@ class JdbcHook(DbApiHook):
            "providers.jdbc" section of the Airflow configuration. If you're enabling these options in Airflow
            configuration, you should make sure that you trust the users who can edit connections in the UI
            to not use it maliciously.
-        4. Patch the ``JdbcHook.default_driver_path`` and/or ``JdbcHook.default_driver_class`` values in the
+        4. Define the "sqlalchemy_scheme" property in the extra of the connection if you want to use the
+           SQLAlchemy engine from the JdbcHook.  When using the JdbcHook, the "sqlalchemy_scheme" will by
+           default have the "jdbc" value, which is a protocol, not a database scheme or dialect.  So in order
+           to be able to use SQLAlchemy with the JdbcHook, you need to define the "sqlalchemy_scheme"
+           property in the extra of the connection.
+        5. Patch the ``JdbcHook.default_driver_path`` and/or ``JdbcHook.default_driver_class`` values in the
            ``local_settings.py`` file.
 
     See :doc:`/connections/jdbc` for full documentation.