How to install custom apt packages?

[msabramo]

I'm new to buildstep, but working with Docker for a bit.

I'm intrigued by the idea of being able to use buildstep, because I have sort of my own version, but it would be nice to use something "standard".

What I would love is to be able to apt-get install packages listed in a requirements.apt file?

Is this something that makes sense to add? Or is it out of scope and should be done with custom buildpack or something? It seems like something a lot of people might want.