Reference a local copy of the release notes in the 'version too old' warning, plus a redirect to the support links

Changed files
+4 -1
+4 -1
default.nix
···
curl https://nixos.org/nix/install | sh
For more information, please see the NixOS release notes at
-
https://nixos.org/nixos/manual.
+
https://nixos.org/nixos/manual or locally at
+
${toString ./doc/manual/release-notes}.
+
+
If you need further help, see https://nixos.org/nixos/support.html
''
else