Improve documentation on settings for allowing removing/reducing regions.

[rushl]

I initially posted that I couldn't reduce/delete a region. I have now discovered that it's a setting. This setting could be highlighted better in the docs. When a print is actively failing and you're trying to save it, it would be a big help to have that information visible at a quick glance down the page. Ideally, this plugin isn't required frequently, but when it is, it's usually needed in a hurry! It is not the time to be subtle.