diff --git a/modules/services/prometheus/default.nix b/modules/services/prometheus/default.nix
index aca8f36..770a1a4 100644
--- a/modules/services/prometheus/default.nix
+++ b/modules/services/prometheus/default.nix
@@ -29,6 +29,7 @@ in
       description = "retention time";
     };
 
+    # a good collections for allerts can be found here: https://samber.github.io/awesome-prometheus-alerts/rules#blackbox
     rules = mkOption {
       type = types.attrsOf
         (types.submodule {