docs(readme): Copy-edit Nix instructions and re-arrange flow
docs(readme): Copy-edit Nix instructions and re-arrange flow

Co-authored-by: Caleb Maclennan <77544cb4d450f4c37e30115c8ae45f943c1f515e@alerque.com>

alerque/sile,alerque/sile,alerque/sile,alerque/sile