nix-files/doc/adding-a-program.md

to ship pkgs.foo on some host, either:

• add it as an entry in suggestedPrograms to the appropriate category in hosts/common/programs/assorted.nix, or
• sane.programs.foo.enableFor.user.colin = true in hosts/by-name/myhost/default.nix

if the program needs customization (persistence, configs, secrets):

• add a file for it at hosts/common/programs/<foo>.nix
• set the options, sane.programs.foo.{fs,persist}

if it's unclear what fs paths a program uses:

• run one of these commands, launch the program, run it again, and diff:
  • du -x --apparent-size ~
  • find ~ -xdev
• or, inspect the whole tmpfs root with ncdu -x /