Make manifest link optional out the gate as well

And point to having to turn that on in the routes.rb file.

Author: dhh

railties/lib/rails/generators/rails/app/templates/app/views/layouts/application.html.erb.tt

@@ -9,7 +9,7 @@
 
     <%%= yield :head %>
 
-    <link rel="manifest" href="/manifest.json">
+    <!-- link rel="manifest" href="/manifest.json" -->
     <link rel="icon" href="/icon.png" type="image/png">
     <link rel="icon" href="/icon.svg" type="image/svg+xml">
     <link rel="apple-touch-icon" href="/icon.png">

railties/lib/rails/generators/rails/app/templates/config/routes.rb.tt

@@ -6,7 +6,7 @@ Rails.application.routes.draw do
   get "up" => "rails/health#show", as: :rails_health_check
 
   <%- unless options.api? -%>
-  # Render dynamic PWA files from app/views/pwa/*
+  # Render dynamic PWA files from app/views/pwa/* (remember to link manifest in application.html.erb)
   # get "service-worker" => "rails/pwa#service_worker", as: :pwa_service_worker
   # get "manifest" => "rails/pwa#manifest", as: :pwa_manifest