Man pages in general

I already owe a man page here (#39), but I'd like to add a few more to the pile. As suggested in https://github.com/void-linux/void-runit/pull/58#issuecomment-767213934, we could have a rc.conf(5), maybe together with rc.local(5) and rc.shutdown(5). These would be mostly transferred over from void-docs, from where we would remove explanations and simply add links to the proper man pages.

The advantage here is that information can be found with just man(1) instead of requiring knowledge of void-docs(1) (or, more realistically, opening a browser). One disadvantage I can think of is that this wouldn't take advantage of eventual translation efforts in void-docs. Leaving the information duplicated wouldn't be terrible either, and we'd still get man pages out of it, which is nice.

Review the existing man-page work referenced by #39, the suggested rc.conf(5), rc.local(5), and rc.shutdown(5) pages, and the corresponding material in void-docs. Done means the selected information is available through man(1), while void-docs removes duplicated explanations and links to the new pages.