IPSec VPN Configuration on Ubuntu 18.04

This was something I had to do repeatedly on all my Linux laptops. I found that you must follow *both* 2 articles listed below in the same order, to get it working!

[1] https://github.com/hwdsl2/setup-ipsec-vpn/blob/master/docs/clients.md#linux

[2] https://github.com/nm-l2tp/NetworkManager-l2tp/issues/38#issuecomment-303052751

The package to install in Ubuntu 18.04 can be found here.