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

[padi]

Summary

Adds documentation for removed AV#content_tag_for and AV#div_for for completion.

Other details

I've also added a :nodoc: for the following methods (since I've accidentally ran into them by using Rdoc) and thought that they still existed as available methods for Rails 5.

[rails-bot]

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[padi]

Seems like the build failure has no relation to the current changes. It shouldn't affect any legitimate test since the changes just involve a documentation and a ruby comment. Didn't use [ci skip] though since I'm still technically modifying a ruby file.