Document triangles

[xeruf]

This threw me off before looking at the code, I was really confused by the appearing triangles:

    // mark too long lines, if there are any left
    textArea.value = textArea.value.replace(/^([^◀\n]{72,}?)(?!◀) /gm, "$1◀ ");

Document it in the readme and website, please :)

[waldyrious]

That's a great point :) I am not really happy with the current behavior, to be honest. I should probably use text or background (highlight) color to mark the extra lengthy passages, rather than an actual triangle character. I'd be happy to review a PR with such a change.

In the meantime, a contribution to the documentation and website copy would be appreciated too. I would eventually do this myself, but I can't promise I'll get around to do it anytime soon.