Consolidate external scripts into this repo

[geerlingguy]

I have two scripts I'd like to consolidate into this repo for easier maintenance/tracking:

1. disk-benchmark.sh
2. sbc-general-benchmark.sh

I could maybe even convert them to Pyinfra... or at least make an easier time converting them for other platforms like macOS (see #96).

[geerlingguy]

To get sbc-general-benchmark.sh running on macOS, btw: https://gist.github.com/geerlingguy/570e13f4f81a40a5395688667b1f79af?permalink_comment_id=5897216#gistcomment-5897216