Clarify unsubscribe route

This adds some context around where the route goes and why it's a singular route to address questions that have come up recently.

Co-authored-by: Hartley McGuire <[email protected]>

Author: 2 people

guides/source/getting_started.md

@@ -2363,10 +2363,17 @@ A subscriber may want to unsubscribe at some point, so let's build that next.
 First, we need a route for unsubscribing that will be the URL we include in
 emails.
 
-```ruby
+```ruby#6
+Rails.application.routes.draw do
+  # ...
+  resources :products do
+    resources :subscribers, only: [ :create ]
+  end
   resource :unsubscribe, only: [ :show ]
 ```
 
+The unsubscribe route is added at the top level and uses the singular `resource` in order to handle routes like `/unsubscribe?token=xyz`.
+
 Active Record has a feature called `generates_token_for` that can generate
 unique tokens to find database records for different purposes. We can use this
 for generating a unique unsubscribe token to use in the email's unsubscribe URL.