Freestyle Line Set not Showing in Blender 2.79 Similar problem as in this other post:

Freestyle line is not showing

Freestyle Line Set should be in Render Layers ( Properties ), but is not Showing in Blender 2.79

Based on Blender 2.79 manual it should be there. Do I need to activate something. I already activated an addon called: FreeStyle Line Style SVG Export, but that didn't help.

https://docs.blender.org/manual/en/dev/render/freestyle/parameter_editor/line_set.html#edge-marks
Got it solved, thanks to this video by Blender Nerd ( Thanks ).

https://www.youtube.com/watch?v=6ItWP3lGBGY

Basically you need to first enable / activate "Freestyle" in the Properties > Render Tab. 

Then you can go to the Properties > Render Layers Tab and you'll see a new section called: Freestyle