Runout Sensor for 2020 rails

I saw Blaiseb's design for a filament sensor, but wanted it mounted on 20x20 rails so did a quick remix.

I removed the existing mount, added a wing (left and right option) as well as modified a few minor (.1-.3 mm) measurements for better fit and filament slot width (reduced to 2.6mm) to ensure the switch is triggered.

I also added a directional arrow for the filament flow direction to ensure it is mounted in the proper direction.

M3 screws are enough to mount with T-nuts. Might want some M3 washers if you have a small headed screw.

You will need a 608 ball bearing and a [roller switch](https://www.tme.eu/se/en/details/wlk-4mini_he/microswitches-snap-action/highly/ss0505a/) and some wire with a plug to get this up and running.

Fusion 360 file provided in case anyone wants to remix further. :)