Improve discoverability of missing required dependencies

[Cyberbeni]

They are printed after the init command finishes. -- This can be easily lost if this runs as part of a larger script that installs more stuff.
They are printed after update runs but if we are already using the latest version then they are not printed.

We could have a new subcommand.
We could add automatic checking to env.sh, so people are notified about issues when opening a new terminal. (Sidenote: the installation guide could be more clear that sourcing env.sh should be added to zshrc/bashrc/etc.,)

edit: Ah, I only set zsh in my konsolerc and not with chsh, so it added env sourcing to .profile based on $SHELL being /bin/bash