fix: suggested command to update flake inputs

the --recreate-lock-file flag is marked as deprecated in the nix docs https://nixos.org/manual/nix/unstable/command-ref/new-cli/nix3-flake-update#opt-recreate-lock-file

flake.nix

@@ -1,7 +1,7 @@
 {
   description = "devshell";
   # To update all inputs:
-  # nix flake update --recreate-lock-file
+  # nix flake update
   inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
   inputs.flake-utils.url = "github:numtide/flake-utils";