Update virtual-machine-scale-sets-maxsurge.md

Author: mimckitt

articles/virtual-machine-scale-sets/virtual-machine-scale-sets-maxsurge.md

@@ -18,6 +18,19 @@ ms.custom: upgradepolicy. maxsurge
 
 Rolling upgrades with MaxSurge can help improve service uptime during upgrade events. With MaxSurge enabled, new instances are created in batches using the latest scale model. When the new instances are fully created and healthy, they begin taking traffic. The scale set then deletes instances in batches matching the old scale set model. The process continues until all instances are brought up-to-date. 
 
+## Prerequisites 
+
+Before configuring a rolling upgrade policy on a Virtual Machine Scale Set with Flexible Orchestration or enabling MaxSurge on either Flexible or Uniform Orchestration deployments, register the feature providers to your subscription.
+
+## Feature Registration
+
+```azurepowershell-interactive
+Register-AzProviderFeature -FeatureName VMSSFlexRollingUpgrade -ProviderNameSpace Microsoft.Compute
+
+Register-AzProviderFeature -FeatureName MaxSurgeRollingUpgrade -ProviderNamespace Microsoft.Compute
+```
+
+
 ## Concepts
 
 > [!NOTE]