Update README.md (#41)

added database management OCID details

knowlege-content/oracle-database/APEX/apm/README.md

@@ -34,6 +34,10 @@ Add this JavaScript code snippet to your APEX application's global page to colle
 ## Create a Custom APEX Dashboard 
 Download this [JSON file](https://github.com/oracle-quickstart/oci-o11y-solutions/blob/0de0d63f61782f04a204e57ea929a313fb1770d2/knowlege-content/oracle-database/APEX/dashboards/apm-rum-apex-dashboard.json) to import this custom dashboard to your Oracle Cloud instance to monitor your APEX application. The video posted above demonstrates how to import your dashboard.
 
+To view the database related data on your dashboard, [enable the Database Management service](https://docs.oracle.com/en-us/iaas/database-management/doc/enable-database-management.html) for that database.
+
+For an on-premises database, use the database management service to first [discover the external database](https://docs.oracle.com/en-us/iaas/database-management/doc/discover-external-database-systems.html) and then find it’s OCID. Next, when you import this APEX dashboard, you can overwrite the OCID in the JSON file with your external database OCID. If you are using an Oracle Autonomous Database, the OCID is automatically overwritten when you import the APEX dashboard. 
+
 ![dashboard-apex](https://github.com/oracle-quickstart/oci-o11y-solutions/assets/106996346/b952ce8c-f920-435b-a14f-c8a8258c5fc3)
 
 ## Integrate with the Database Management Service on Oracle Cloud