How to create gatewaysubnet and which network should be a subnet through Resource Manager

From saurabh @tsaurabh9 via Twitter

Can i get help in creating Site to Site VPN through Resource manager. i'm referring a link https://azure.microsoft.com/en-us/documentation/articles/vpn-gateway-create-site-to-site-rm-powershell/

but i have doubt on gatewaysubnet how to create it and which network should be a gateway subnet. Because in creating Site Site Vpn in Classic model deployment it gets created automatically but in resource manager which subnet shall i choose as gatewaysubnet

I created a Resource group and one virtual network with two subnets. but i'm getting confused on a statement in a page "It's important to create one subnet named specifically GatewaySubnet. If you name it something else, your connection configuration will fail."

Thanks,

@AzureSupport