feat: add /var/src to NIX_PATH

configs/default.nix

@@ -74,6 +74,9 @@ in
         cursor = { name = "capitaine-cursors"; package = pkgs.capitaine-cursors; };
       };
     }
+    {
+      nix.nixPath = [ "/var/src" ];
+    }
     {
       nixpkgs.config = {
         allowUnfree = true;