Updating statement around discovery using Replication appliance.

Physical Servers are not discovered until mobility agent is installed on the servers. Added statement with recommendation to use Azure Migrate appliance for discovery and assessment.

Author: ravibak

articles/migrate/tutorial-migrate-physical-virtual-machines.md

@@ -147,10 +147,13 @@ The first step of migration is to set up the replication appliance. To set up th
 
     ![Finalize registration](./media/tutorial-migrate-physical-virtual-machines/finalize-registration.png)
 
-It may take some time after finalizing registration until discovered machines appear in Azure Migrate: Server Migration. As VMs are discovered, the **Discovered servers** count rises.
+Mobility service agent needs to  be installed on the serverrs to get them discovered using replication appliance. Discovered machines appear in Azure Migrate: Server Migration. As VMs are discovered, the **Discovered servers** count rises.
 
 ![Discovered servers](./media/tutorial-migrate-physical-virtual-machines/discovered-servers.png)
 
+> [!NOTE]
+> It is recommended to perform discovery and asessment prior to the migration using the Azure Migrate: Discovery and assessment tool, a separate lightweight Azure Migrate appliance. You can deploy the appliance as a physical server, to continuously discover servers and performance metadata. For detailed steps, see [Discover physical servers](tutorial-discover-physical.md).
+
 
 ## Install the Mobility service
 
@@ -369,4 +372,4 @@ After you've verified that the test migration works as expected, you can migrate
 
 ## Next steps
 
-Investigate the [cloud migration journey](/azure/architecture/cloud-adoption/getting-started/migrate) in the Azure Cloud Adoption Framework.
+Investigate the [cloud migration journey](/azure/architecture/cloud-adoption/getting-started/migrate) in the Azure Cloud Adoption Framework.