As pointed out in https://github.com/denoland/deno/issues/21067 , it's
confusing that `deno doc --lint mod.ts` outputs the documentation to
stdout on success. Instead, it would be better if it outputted how many
files were checked similar to what `deno lint` does on success. It still
outputs the documentation if `--lint` or `--html` are provided so this
is non-breaking.
