Authentication, Generators, Routing and more

I went through this [Simple Authentication](https://medium.com/@andreichernykh/phoenix-simple-authentication-authorization-in-step-by-step-tutorial-form-dc93ea350153) tutorial over the weekend and would highly recommend it.

+ It shows you some nice implementations of the [`mix phoenix.gen.model`](https://hexdocs.pm/phoenix/Mix.Tasks.Phoenix.Gen.Model.html)
+ It introduces you to [Guardian](https://github.com/ueberauth/guardian) for authentication
+ Teaches you some nice patterns with using plugs
+ Teaches you a few cool tricks (I learnt about [scrub params](https://hexdocs.pm/phoenix/Phoenix.Controller.html#scrub_params/2) which I wish I knew about for my last project)
+ Shows you a really nice construction of the [`web/router.ex`](https://github.com/madeinussr/phoenix_simple_auth/blob/master/web/router.ex) file

It's well worth spending 30 mins going through this tutorial

Open the linked Simple Authentication tutorial and review its examples of generators, Guardian, plugs, and web/router.ex. The issue does not identify a documentation change, file to edit, test to run, or concrete definition of done, so no contribution can be started from the issue alone.

Written by the indexing model from the issue text.