1: Set your brush size to 2 and colour to white.
2: Whip out the pen tool and draw your door line.
3: With the pen still selected, click your 2nd button on your mouse and select stroke. Select it to stroke using the brush tool.
4: You have a white line now. Duplicate it and then invert the duplicates colours so it turns into black.
5: Basing on the direction of your main light, nudge the shite layer underneath a couple of pixels to create the highlight reflection of your door line.
6: Adjust opacity and blend mode, if necessary.
7: Use the eraser tool (or masking) to make the door line thinner in some areas. This is based on the angle and the perspective.