Use remote url from docs

[dszakallas]

As reported in #47 , the remote url does not work anymore. This PR changes it to https://downloads.nordcdn.com/configs/archives/servers/ovpn.zip as documented on https://support.nordvpn.com/Connectivity/Linux/1061938702/How-to-connect-to-NordVPN-using-Linux-Network-Manager.htm