Yubikey 5C case with pivot

A slightly remixed version of the keychain case for the [Yubikey 5C](https://www.yubico.com/product/yubikey-5-series/yubikey-5c-nfc/). The original versions had a hole that was too small for my keyring. When I made the hole larger, it just barely fit, but the case was really stiff on my keychain and made the whole thing awkward in my pocket.

I modified it slightly so that I could use a 9mm [D-ring](https://www.amazon.com/dp/B09H4B73FC) and a small [pivot](https://www.amazon.com/gp/product/B09YXYPMYR). These make the case more flexible if you keep it in your pocket.