Move doc/markup_reference.rb to doc/rdoc

[BurdetteLamar]

No description provided.

[peterzhu2118]

I'm not sure what problem this is supposed to solve. It just includes the file doc/markup_reference.rb in the built .gem file that is built, but markup_reference.rb is just documentation, so I don't see why it's included in the built gem.

[BurdetteLamar]

See https://ruby.slack.com/archives/C02A3SL0S/p1658264615750489. I think this PR solves the problem.

[peterzhu2118]

I don't see how this PR solves the problem. docs.ruby-lang.org is built from the ruby/ruby repository. I don't think this will sync the doc/markup_reference.rb file to the ruby/ruby repository.

[BurdetteLamar]

Somehow, doc/ files from ruby/csv get into ruby/ruby, but doc/ files from ruby/rdoc don't. If this is not the way, do you know how to make that happen?

[peterzhu2118]

From what I can tell, it looks manually sync'd, not automatically. Looks like that tool to do the sync is in tool/sync_default_gems.rb and you can run it using tool/sync_default_gems.rb -a rdoc.

[BurdetteLamar]

So I would add to the clause when "rdoc" in that program?
`

[peterzhu2118]

It would be a good idea to move all the files in the doc directory of RDoc to doc/rdoc to prevent name collisions. Then you can add something like:

cp_r("#{upstream}/doc/rdoc", "doc")

[BurdetteLamar]

It would be a good idea to move all the files in the doc directory of RDoc to doc/rdoc to prevent name collisions. Then you can add something like:

cp_r("#{upstream}/doc/rdoc", "doc")

Done.

[peterzhu2118]

Can you change the PR title to match the changes? Otherwise it looks good.