Also anyone who things typing commands in terminal, even if they seem easy to you, is easier for a regular user than running a Gui installer they get from a website, has never really had to work with a non techy user. Try telling people to 'run ver in a command prompt to find out the version number', and see how they respond - I'm deliberately using a Windows example to illustrate the point.
Those types of users have ZERO reason to ever use the command line in Linux.
Do you think those are the types of users installing Docker ? If someone installing docker can't figure out some basic instructions on how to install from the companies own Docker repository... perhaps they should find a new line of work coding isn't for them.
BTW your install instructions where for Ubuntu... and seem to be instructions on how to add their own repository first. (which they use hhtps... so they tell you how to do that).
It most distros docker is a supported software already in the database... and frankly one thing I don't like about Ubuntu is all the software projects / companies that think they should bypass the normal ways of doing things with PPAs and secondary repositories. (as perhaps the largest current distro that seems to be a trend). In Arch its click install click remove. (current version in Arch is 17.06... newest windows version I see on their site seems to be 17.04... so I say win for Arch Linux. )
The point I was on about earlier was that the command line isn't rocket science. Its not hard to figure out really... the vast majoirty of users will never ever need it for anything. Still most people can figure it out. Its no harder then it was back when every average user had to deal with Windows 3.1, and MS-DOS as it was just a shell.
Comptuers have gotten easier to use over the years... but perhaps its time we accept a bit more complication into our computing lives. Kids have no issues with this stuff. Learning the Linux command line basics like LS CP MV and the like is a good thing for everyone. Older users that really can't type ver into a windows prompt don't ever need to touch a command line in Linux, cause sure good luck getting them to type uname -a... for everyone else ya why not learn the basics. They also apply to OSX BSD Unix ect... so not bad things to know.