ANPEEE: BGP Prefix not required on Address Prefix

Adding the same info from Portal doc to PS doc, stating that is not required to use the AddressPrefix field if BGP is configured.

Author: jofons

articles/vpn-gateway/vpn-gateway-bgp-resource-manager-ps.md

@@ -182,6 +182,7 @@ A couple of things to note regarding the local network gateway parameters:
 
 * The local network gateway can be in the same or different location and resource group as the VPN gateway. This example shows them in different resource groups in different locations.
 * The prefix you need to declare for the local network gateway is the host address of your BGP Peer IP address on your VPN device. In this case, it's a /32 prefix of "10.51.255.254/32".
+* You can also leave the prefix empty if you're using BGP to connect to this network. Azure VPN gateway will internally add a route of your BGP peer IP address to the corresponding IPsec tunnel.
 * As a reminder, you must use different BGP ASNs between your on-premises networks and Azure VNet. If they're the same, you need to change your VNet ASN if your on-premises VPN device already uses the ASN to peer with other BGP neighbors.
 
 #### 2. Create the local network gateway for Site5