Recommended installation of docker after deprecation of snap

[eedrah]

Given the recent deprecation notice, I feel it would be a good idea to include recommended installation instructions of docker that users should use instead of Snap.

[seemethere]

I'd recommend reading through the documentation @ https://docs.docker.com/install/linux/docker-ce/ubuntu

Or if you'd just like a quick start you can use our convenience script at https://get.docker.com