docs: suggest to use 0.3.0 tagged release of lanzaboote rather than m…

…aster

This is to avoid people relying on dangerous development branches.

Retake of #207…

docs/QUICK_START.md

@@ -103,7 +103,7 @@ secret key so that only root can read it.
 Add `lanzaboote` as a dependency of your niv project and track a stable release tag (https://github.com/nix-community/lanzaboote/releases).
 
 ```console
-$ niv add nix-community/lanzaboote -r v0.2.0 -v 0.2.0
+$ niv add nix-community/lanzaboote -r v0.3.0 -v 0.3.0
 Adding package lanzaboote
   Writing new sources file
 Done: Adding package lanzaboote
@@ -152,7 +152,7 @@ Boot stack.
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
 
     lanzaboote = {
-      url = "github:nix-community/lanzaboote";
+      url = "github:nix-community/lanzaboote/0.3.0";
 
       # Optional but recommended to limit the size of your system closure.
       inputs.nixpkgs.follows = "nixpkgs";