docs: add a warning in migration-guide for third party installation (#2527)

Signed-off-by: Ludovic Ortega <ludovic.ortega@adminafk.fr>

Author: M0NsTeRRR

docs/migration-guide.mdx

@@ -200,6 +200,11 @@ Summary of changes :
 </Tabs>
 
 ## Third-party installation methods
+
+:::warning
+Third-party installation methods are maintained by the community. The Seerr team is not responsible for these packages.
+:::
+
 ### Nix
 
 Waiting for https://github.com/NixOS/nixpkgs/pull/450096 and https://github.com/NixOS/nixpkgs/pull/450093