This guide is a bit outdated now. Please have a look at Spaceinvader one's video about docker. It is current and quite detailed.
P.S. He is spaceinvaderone here on the UnRAID forums.
Video guides are at the bottom of this post.
Well I just figured out how to set up docker and I am completely new to docker so I decided to make a quick guide to help other people who are new.
p.s. this is for unraid 6.0 beta 10 and up i think, correct me