Adding the first thoughts on user signup

The describe do, it do is the foundational structure of rspec.
"Describe" provides the context in which we are running our specs.
"It" is the context for an expectation/assertion.
Adding first spec step for viewing singup page

By using `rake routes` I was able to inspect what the existing routes
were for my Rails application. It looks like '/users/sign_in' is the
path to the Devise signup page.