docs: add warning

Signed-off-by: Raju Udava <86527202+dstala@users.noreply.github.com>

Author: dstala

content/self-hosting/installation/nix.mdx

@@ -5,6 +5,8 @@ tags: ['Open Source', 'Nix', 'NixOS']
 keywords : ['NocoDB installation', 'NocoDB one command installation', 'NocoDB prerequisites']
 ---
 
+<Callout type="warning"> Not supported since v0.264.6 / Sep 2025 </Callout>
+
 ### Basic Setup
 The NixOS module is the recommended method for installing and configuring NocoDB on NixOS. We advise using Flakes for this process. The NixOS module will install NocoDB and create a corresponding systemd service