Documenting lib/debug.rb

[dpulliam]

Hey y'all, so I wanted to try submitting my first patch to Ruby and I thought documentation would be a good way to start.

For now I am trying to document #thread_list_all().

I hope to document more of the class but I wanted to start small to get the process down.

[dpulliam]

I haven't opened a PR yet because I planned on just submitting a patch to the tracker, but here is a link to my most recent commit if you're interested.

dpulliam@5b5d91e

here's the link to my current patch in the issue tracker https://bugs.ruby-lang.org/issues/11580