Added create master key

Author: jovanpop-msft

articles/synapse-analytics/quickstart-sql-on-demand.md

@@ -61,6 +61,9 @@ To run queries using SQL on-demand, create data source that SQL on-demand can us
 Execute the following code snippet to create data source used in samples in this section:
 
 ```sql
+-- create master key that will protect the credentials:
+CREATE MASTER KEY ENCRYPTION BY PASSWORD = <enter very strong password here>
+
 -- create credentials for containers in our demo storage account
 CREATE DATABASE SCOPED CREDENTIAL sqlondemand
 WITH IDENTITY='SHARED ACCESS SIGNATURE',