undervolt: clarify that the service is unofficial

The original warning almost made it sound like the service was made by or
somehow connected to Intel which is not the case

nixos/modules/services/hardware/undervolt.nix

@@ -25,8 +25,11 @@ let
 in
 {
   options.services.undervolt = {
-    enable = mkEnableOption
-      "Intel CPU undervolting service (WARNING: may permanently damage your hardware!)";
+    enable = mkEnableOption ''
+       Undervolting service for Intel CPUs.
+
+       Warning: This service is not endorsed by Intel and may permanently damage your hardware. Use at your own risk!
+    '';
 
     verbose = mkOption {
       type = types.bool;