nixos/home-assistant: NixOS is an unsupported installation method

Trying to steer NixOS users away from reporting bugs to the upstream,
when they don't have the capacity to support bugs that could be the
result of our downstreaming setup.

nixos/modules/services/misc/home-assistant.nix

@@ -66,7 +66,9 @@ in {
   meta.maintainers = teams.home-assistant.members;
 
   options.services.home-assistant = {
-    enable = mkEnableOption "Home Assistant";
+    # Running home-assistant on NixOS is considered an installation method that is unsupported by the upstream project.
+    # https://github.com/home-assistant/architecture/blob/master/adr/0012-define-supported-installation-method.md#decision
+    enable = mkEnableOption "Home Assistant. Please note that this installation method is unsupported upstream";
 
     configDir = mkOption {
       default = "/var/lib/hass";