I see it used frequently ingame and I want to know how I can do it in my favorite image editor.

You mean scan lines?
Google something like, "scan line transparent", find a suitable image with alpha then just paste it onto your picture.

The 'TV Lines' are, like Glitch said, called scan-lines.
They are transparent or semi transparent black lines repeating across the screen.
If you can wait until I get back to my computer, I'll send you and image to overlay to create them.