docs: add missing migration steps (#2376)

docs/getting-started/third-parties/nixpkg.mdx

@@ -10,8 +10,21 @@ import Tabs from '@theme/Tabs';
 import TabItem from '@theme/TabItem';
 
 # Nix Package Manager
+:::danger
+This method has not yet been updated for Seerr and is currently a work in progress.
+You can follow the ongoing work on these pull requests:
+  - https://github.com/NixOS/nixpkgs/pull/450096
+  - https://github.com/NixOS/nixpkgs/pull/450093
+:::
+
+<!--
 :::warning
 Third-party installation methods are maintained by the community. The Seerr team is not responsible for these packages.
 :::
 
+:::warning
+This method is not recommended for most users. It is intended for advanced users who are using NixOS distribution.
+:::
+
 Refer to [NixOS documentation](https://search.nixos.org/options?channel=25.05&query=seerr)
+-->