Update deployment-guidance.md

Author: mihaelablendea

docs/big-data-cluster/deployment-guidance.md

@@ -142,7 +142,7 @@ The following environment variables are used for security settings that are not
 | **CONTROLLER_USERNAME** | Required |The username for the cluster administrator. |
 | **CONTROLLER_PASSWORD** | Required |The password for the cluster administrator. |
 | **MSSQL_SA_PASSWORD** | Required |The password of SA user for SQL master instance. |
-| **KNOX_PASSWORD** | Required |The password for Knox user. |
+| **KNOX_PASSWORD** | Required |The password for Knox **root** user. Note than in a basic authentication setup only user supported for Knox is **root**.|
 | **ACCEPT_EULA**| Required for first use of `azdata`| Requires no value. When set as an environment variable, it applies EULA to both SQL Server and `azdata`. If not set as environment variable, you can include `--accept-eula` in the first use of `azdata` command.|
 | **DOCKER_USERNAME** | Optional | The username to access the container images in case they are stored in a private repository. See the [Offline deployments](deploy-offline.md) topic for more details on how to use a private Docker repository for big data cluster deployment.|
 | **DOCKER_PASSWORD** | Optional |The password to access the above private repository. |
@@ -165,6 +165,10 @@ SET MSSQL_SA_PASSWORD=<password>
 SET KNOX_PASSWORD=<password>
 ```
 
+> [!NOTE]
+> You must use **root** user for Knox gateway with the above password. **root** is the only user supported for in this basic authentication (username/password) setup. For SQL Server master, username provisioned to be used with the above password is **sa**.
+
+
 After setting the environment variables, you must run `azdata bdc create` to trigger the deployment. This example uses the cluster configuration profile created above:
 
 ```bash