Binary Nix tarballs available

Our continuous build system, Hydra, now produces binary tarball distributions of Nix for Mac OS X (Darwin), FreeBSD and Linux. The tarballs contain all dependencies of Nix, making it a lot easier to install Nix on those platforms. To install, download a binary tarball, unpack it in the root directory, then run nix-finish-install. See the manual for more information.