K40 Mirror Shims

I've finally got round to aligning the mirrors in my K40 laser cutter. Using the [mirror alignment guide](https://k40laser.se/lens-mirrors/mirror-alignment-the-ultimate-guide/) on k40laser.se, I needed to raise mirror 2 a little to get the alignment perfect. I tried using washers, but that was just too awkward for my fat fingers, so I designed and printed these shims instead.

There's a range of shims, from 2.0mm to 4.0mm in 0.5mm increments, which I found was enough range for me.