Upgraded bracket for DIYnder

This is just a modified bracket to fit the DIYnder from Friendly Beans (on MMF), which I find very useful for mounting it. Included is the slotted bar, which MMF didn't seem to like being posted on its own. This is helpful as it means the screws don't have to be removed to take the bracket on and off. I have printed it in PETG, but PLA should be fine too.