repro-env: Documented and reproducible build environments

[cen]

> You can think of it as "Cargo.toml/Cargo.lock but for GNU/Linux build 
> environments".

Interesting tool. I was trying to figure out if this could help me 
produce reproducible OCI images but the workflow seems to work against me.

Is there a clever way repro-env could produce a base image for build 
and/or runtime step of my Dockerfile or am I simply misusing it?