Break test for new sign up route => /sign_ups routes to SignUpsController#index

- Test failing
- In routes.rb, need to update resources :sign_ups => only: [:new] becomes
  only: [:index]
Refactor routes for new sign ups => resources :sign_ups, only: [:index]

- Failing test => Signing up with email displays success message
- Failing test => SignUpsController#new sets @sign_up
Refactor failing test => SignUpsController#index sets @sign_up

- failure:

 Failure/Error: get :index
 AbstractController::ActionNotFound:
   The action 'index' could not be found for SignUpsController
Update SignUps Controller => #new becomes #index

- Failing test => SignUpsController#index sets @sign_up

  - failure

   ActionView::MissingTemplate:
     Missing template sign_ups/index, application/index with {:locale=>[:en], :formats=>[:html], :handlers=>[:erb, :builder, :raw, :ruby, :jbuilder, :coffee]}. Searched in:
       * "#<RSpec::Rails::ViewRendering::EmptyTemplatePathSetDecorator:0x007f8ee0885e48>"
Green:  SignUpsController#index sets @sign_up

- Red:  Signing up with email displays success message
Red:  Signing up with email displays success message

1) Signing up with email displays success message
   Failure/Error: background { visit sign_ups_path }
   ActionView::Template::Error:
     undefined method `create_or_update_sign_up_path' for #<#<Class:0x007fd06a139150>:0x007fd06a138480>
Add route to create or update sign ups

-----TEST TO FIX-----

1) Signing up with email displays success message
   Failure/Error: background { visit sign_ups_path }
   ActionView::Template::Error:
     No route matches {:id=>#<SignUp id: nil, email: nil, created_at: nil, updated_at: nil>} missing required keys: [:id]