[Doc] Link to doc/contributing.rdoc from CONTRIBUTING.md

[kachick]

https://github.com/ruby/ruby/blob/c7e6914b3947cdf0e9c0d28d1162a084d0138887/doc/contributing.rdoc looks the active one of How to contribute. So adding link in CONTRIBUTING.md might help someone like me 🙏

In my case...
I often forgot How to test specific test file with the built ruby?
Nothing in README. And I can't find it in https://bugs.ruby-lang.org/projects/ruby/wiki/HowToContribute

But the rdoc describes as below.

This is also how you can run a specific test from our build dir:

make test-all TESTS=drb/test_drb.rb

It solved all. ☺️

[nobu]

Shouldn't it be a link to the local file?

Suggested change

	[contributing.rdoc]: https://github.com/ruby/ruby/blob/master/doc/contributing.rdoc
	[contributing.rdoc]: rdoc-ref:contributing.rdoc

[kachick]

Oh, I don't know the feature rdoc-ref! 😮
Is it a RDoc feature? So can't we use it in Markdown?

https://github.com/ruby/ruby/blob/db0ad48309edae28a65e3d18e9b3a15753eda777/doc/NEWS-3.0.0.md

Above doc having similar style, it shows GFM as below

And this change so on...

c5795c3
https://github.com/ruby/ruby/blob/c5795c37e61de30df15501e48ad61167e5841953/CONTRIBUTING.md

Do we need to handle .md files as a rdoc in this repository?

[nobu]

It is possible in also RDoc's Markdown, but GitHub doesn't support it of course, even in *.rdoc files.
In RDoc, "rdoc-ref:" link generates a URL from the path under the certain rule.
I made ruby/rdoc#800 to enable it for explicit references without the prefix.
Once this gets applied, the above link no longer needs the prefix.

[kachick]

Thank you for the rdoc improvement! 😂

I have applied your suggestion cc779f4

$ rdoc --version
6.3.0
$ rdoc CONTRIBUTING.md --op tmp-rdoc
$ open tmp-rdoc/CONTRIBUTING_md.html

It looks not a link 🤔
It makes same even if adding doc/ prefix as rdoc-ref:doc/contributing.rdoc.
But https://docs.ruby-lang.org/en/master/doc/NEWS-3_0_0_md.html shows as link.

Hmm… Definitely I do not know something about rdoc 🙇

[nobu]

ruby/rdoc#800 is not merged yet.
And it doesn't change the result for "rdoc-ref:", the line needs to be [doc/contributing.rdoc]: doc/contributing.rdoc without the schema prefix.

[kachick]

https://github.com/ruby/ruby/blob/f2ad63b361236df26aae33a19c851f106e752b1b/CONTRIBUTING.md

Ah… I may understand it finally. 😓
f2ad63b is this correct understanding?
I didn't know Markdown can use relative path, This is so useful!

[nobu]

Exactly.

[kachick]

Thank you! 🙏

Of course I am appreciating to ruby/rdoc#800 😂