Update doc/manual/src/glossary.md
Update doc/manual/src/glossary.md

Co-authored-by: Valentin Gagarin <edf0856f6febb9f05344b3b3b0060e83cede9be8@tweag.io>
NixOS/nix,NixOS/nix,NixOS/nix,NixOS/nix,NixOS/nix