doc/stdenv: improve autoPatchelfHook description
doc/stdenv: improve autoPatchelfHook description

* Add id
* Mention rpath
* The control variables do not really have to be env vars (though without structuredAttrs there is not a difference)

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs