Merge pull request #29884 from padi/update_rails_5_upgrade_guide

Updates Rails upgrade guide on `ActionView::Helpers::RecordTagHelper`

actionview/lib/action_view/helpers/record_tag_helper.rb

 module ActionView
   module Helpers
     module RecordTagHelper
-      def div_for(*)
+      def div_for(*) # :nodoc:
         raise NoMethodError, "The `div_for` method has been removed from " \
           "Rails. To continue using it, add the `record_tag_helper` gem to " \
           "your Gemfile:\n" \
@@ -9,7 +9,7 @@ def div_for(*)
           "Consult the Rails upgrade guide for details."
       end
 
-      def content_tag_for(*)
+      def content_tag_for(*) # :nodoc:
         raise NoMethodError, "The `content_tag_for` method has been removed from " \
           "Rails. To continue using it, add the `record_tag_helper` gem to " \
           "your Gemfile:\n" \

guides/source/upgrading_ruby_on_rails.md

@@ -276,6 +276,16 @@ You can now just call the dependency once with a wildcard.
 <% # Template Dependency: recordings/threads/events/* %>
 ```
 
+### `ActionView::Helpers::RecordTagHelper` moved to external gem (record_tag_helper)
+
+`content_tag_for` and `div_for` has been removed in favor of just using `content_tag`. To continue using it, add the `record_tag_helper` gem to your Gemfile:
+
+```ruby
+gem 'record_tag_helper', '~> 1.0'
+```
+
+See [#18411](https://github.com/rails/rails/pull/18411) for more details.
+
 ### Removed Support for `protected_attributes` Gem
 
 The `protected_attributes` gem is no longer supported in Rails 5.