Add missing example for cookies.encrypted [ci skip]

actionpack/lib/action_dispatch/middleware/cookies.rb

@@ -77,6 +77,12 @@ def cookies_digest
   #   # It can be read using the signed method `cookies.signed[:name]`
   #   cookies.signed[:user_id] = current_user.id
   #
+  #   # Sets an encrypted cookie value before sending it to the client which
+  #   # prevent users from reading and tampering with its value.
+  #   # The cookie is signed by your app's `secrets.secret_key_base` value.
+  #   # It can be read using the encrypted method `cookies.encrypted[:name]`
+  #   cookies.encrypted[:discount] = 45
+  #
   #   # Sets a "permanent" cookie (which expires in 20 years from now).
   #   cookies.permanent[:login] = "XJ-122"
   #
@@ -89,6 +95,7 @@ def cookies_digest
   #   cookies.size                  # => 2
   #   JSON.parse(cookies[:lat_lon]) # => [47.68, -122.37]
   #   cookies.signed[:login]        # => "XJ-122"
+  #   cookies.encrypted[:discount]  # => 45
   #
   # Example for deleting:
   #