Vertical and horizontal lines for better precision

Feature Description

Hi there,

Awesome app, I must say. I have an idea for a feature which would make it even better, I haven't found it in the configuration or in other feature requests.

Similar apps to this one show both horizontal and vertical lines intersecting at the mouse position, which is nice to know where to crop so as not to resize the rectangle later on. I don't think it wouldn't be too difficult either.

Anyway, thanks a lot! Gonzalo

PS: the fourth bullet point of the Feature Request guideline here in Github has a typo, it says "pictrure"