Alternative doctoc watermark setting

[acovaci]

Hey, thanks for the work here, super cool. I used the functionality in my markdown files, and noticed the generated with doctoc watermark. I personally think it is unsightly, and a bit aggressive for a watermark, but in the spirit of what your intent is, I would not want to remove the doctoc watermark entirely.

So I'm proposing a compromise: add a setting that can convert the watermark to an HTML comment. That way, devs can still see the link to your project, and packages can still include it, but it wouldn't pollute the documentation files themselves.

P.S.: I know I can remove the watermark using a --title option, this is more of a feature request so I don't have to full on remove it.

Thanks