add nixpkgs override to allow unfree packages

flake.nix

@@ -38,5 +38,21 @@
           title = "Julian's dotfiles";
         };
       };
+
+      # The attribute set specified here will be passed directly to NixPkgs when
+      # instantiating the package set.
+      channels-config = {
+        # Allow unfree packages.
+        allowUnfree = true;
+
+        # Allow certain insecure packages
+        # permittedInsecurePackages = [ "firefox-100.0.0" ];
+
+        # Additional configuration for specific packages.
+        config = {
+          # For example, enable smartcard support in Firefox.
+          # firefox.smartcardSupport = true;
+        };
+      };
     };
 }