env/defaults.env specifies `EDITOR=vim`, but by default some alternative popular options like `nano` are not installed in the container. To allow some user freedom in changing this without bloating the container image, I propose adding some environment variable that'd install any extra programs at the start-up, which could cover more useful use-cases than just the editor change that prompted the idea. It could just run something like this on startup: > apt-get update && apt-get install -y $(APT_INSTALL_PACKAGES) ...assuming the APT_INSTALL_PACKAGES env var is defined and non-empty (with space-separated list of packages to install), the exact name of the env var is TBD, it doesn't really matter. Note: you need to run apt(-get) update first, otherwise the package lists are going to be outdated, and thus old package versions will be gone from mirrors and result in 404 upon download attempt of packages!