Add rust overlay to nixpkgs

Author: tilpner

nixpkgs.nix

@@ -5,5 +5,14 @@ import <nixpkgs> {
         url = https://github.com/nix-community/NUR/archive/master.tar.gz;
       })) {};
     })
+
+    (import "${builtins.fetchTarball {
+      url = https://github.com/mozilla/nixpkgs-mozilla/archive/master.tar.gz;
+    }}/rust-overlay.nix")
+
+    (self: super: {
+      inherit (super.nur.repos.tilpner.pkgs)
+        bitflip kernelConfig;
+    })
   ];
 }