writeScript: fix docstring

Fixes #59299

See:
https://github.com/NixOS/nixpkgs/commit/b23dbb1a5dffbfa3abb47fcd0f1579ac2e6f29fc

pkgs/build-support/trivial-builders.nix

@@ -107,10 +107,15 @@ rec {
   writeTextDir = name: text: writeTextFile {inherit name text; destination = "/${name}";};
 
   /*
-   * Writes a text file to /nix/store/<store path> and marks the file as executable.
+   * Writes a text file to /nix/store/<store path> and marks the file as
+   * executable.
+   *
+   * If passed as a build input, will be used as a setup hook. This makes setup
+   * hooks more efficient to create: you don't need a derivation that copies
+   * them to $out/nix-support/setup-hook, instead you can use the file as is.
    *
    * Example:
-   * # Writes my-file to /nix/store/<store path>/bin/my-file and makes executable
+   * # Writes my-file to /nix/store/<store path> and makes executable
    * writeScript "my-file"
    *   ''
    *   Contents of File