doc: use evaluating instead of iterating

flake.nix

···
       # is used here as a substitute attribute name for `packages`. The problem
       # with `packages` is that it makes operations like `nix flake show
       # nixpkgs` unusably slow due to the sheer number of packages the Nix CLI
-      # needs to iterate through. But when the Nix CLI sees a `legacyPackages`
-      # attribute it displays `omitted` instead of iterating through all
-      # packages, which keeps `nix flake show` on Nixpkgs reasonably fast,
-      # though less information rich.
+      # needs to evaluate. But when the Nix CLI sees a `legacyPackages`
+      # attribute it displays `omitted` instead of evaluating all packages,
+      # which keeps `nix flake show` on Nixpkgs reasonably fast, though less
+      # information rich.
       legacyPackages = forAllSystems (system: import ./. { inherit system; });
 
       nixosModules = {