Consolidate external scripts into this repo

I have two scripts I'd like to consolidate into this repo for easier maintenance/tracking: 1. [`disk-benchmark.sh`](https://github.com/geerlingguy/pi-cluster/blob/master/benchmarks/disk-benchmark.sh) 2. [`sbc-general-benchmark.sh`](https://gist.github.com/geerlingguy/570e13f4f81a40a5395688667b1f79af) I could maybe even convert them to Pyinfra... or at least make an easier time converting them for other platforms like macOS (see #96).