Switches in code vs README

[knutsenm]

Leftover questions from #565 are:

I was going to suggest the internal equivalent of standardrb --todo /dev/null, but then I noticed that

• that option, and --config, have both been dropped from the README (although they're still in the code), and
• when I try it, I get an error: it's being passed through to rubocop, which doesn't recognize it; a separate bug?

The --config option does seem to work, perhaps because Standard::MergesSettings#without_banned strips it.

Originally posted by @knutsenm in #565 (comment)