Fix admonish

Author: meator

nix-book.sh

@@ -3,4 +3,4 @@
 #! nix-shell -p bash mdbook mdbook-toc mdbook-admonish
 #! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs/tarball/nixos-24.05
 
-exec ./book.sh "$@"
+exec sh ./book.sh "$@"