Update PS command documentation (#14663)

Author: Nilambari

src/Network/Network/help/Set-AzVirtualNetworkGateway.md

@@ -265,6 +265,28 @@ The third command assigns the address list into addresslist1.
 The fourth command created a PSIpConfigurationBgpPeeringAddress object.
 The fifth command set this new created PSIpConfigurationBgpPeeringAddress to IpConfigurationBgpPeeringAddresses and update the gateway.
 
+### Example 6: Delete multiple expired VpnClientRootCertificates of an existing virtual network gateway
+```
+PS C:\>$Gateway=Get-Azvirtualnetworkgateway -ResourceGroupName "ResourceGroup001" -Name "Gateway001"
+
+PS C:\>$rootCerts=$Gateway.VpnClientConfiguration.VpnClientRootCertificates
+
+PS C:\>$rootCerts.Count
+PS C:\>$rootCerts[0]
+PS C:\>$rootCerts[1]
+PS C:\>$rootCerts.Remove($rootCerts[1])
+
+PS C:\>$Gateway1 = Set-AzVirtualNetworkGateway -VirtualNetworkGateway $Gateway -VpnClientRootCertificates $rootCerts
+
+```
+
+The first command gets a virtual network gateway named Gateway01 that belongs to resource group ResourceGroup001 and stores it to the variable named $Gateway
+The second command gets all the root certificates on VirtualNetworkGateway and save it to another variable $rootCerts
+The third command shows total existing root certs on VirtualNetworkGateway. 
+The forth & fifth commands print root certificates at those corresponding indices for customer to see which ones they want to delete.
+The sixth command removes expired root certificate by using that index e.g. here 1. Repeat same steps to remove multiple expired certificates from variable: $rootCerts
+The seventh command updates VirtualNetworkGateway to set valid root certificates i.e. certificates that exists in variable: $rootCerts
+
 ## PARAMETERS
 
 ### -AadAudienceId