A short summary of kicads limitations.
In kicad 4.0.x (will stay the same in kicad 5) you can not use the footprint editor to put drawings onto the edge cuts layer. But kicad (pcb_new) supports footprints that have edge cuts drawings.
The discussion about this is in https://bugs.launchpad.net/kicad/+bug/1251393
I don’t think there is a valid reason for this limitation. Luckily the devs agree and this will change after kicad 5 (as the discussion mainly happened after the feature freeze for kicad 5)
So the only option to get a footprint with any drawing on the edge cuts layer is by using some external tool. Stepup is a good idea for more complex outlines. The python footprint generator if you want to generate a lots of similar footprints (Example a series of edge connectors).
For simple outlines it might be fastest to design the footprint normally in the footprint editor. Put the drawing for what you want on the edge cuts layer onto an otherwise unused layer and use a text editor with the replace feature to change the layer name.
Be aware that opening a footprint with anything on the edge cuts layer with the footprint editor will move that drawing to a different layer (I think it will move it to the F.SilkS layer. This might be version dependent.)
So you can not use the footprint editor to inspect your footprint.