lib.trivial: Change comment type before concat function

C-style comment was being picked up by nixdoc as a documentation comment for the function.

lib/trivial.nix

@@ -61,11 +61,11 @@ rec {
   pipe = val: functions:
     let reverseApply = x: f: f x;
     in builtins.foldl' reverseApply val functions;
-  /* note please don’t add a function like `compose = flip pipe`.
-     This would confuse users, because the order of the functions
-     in the list is not clear. With pipe, it’s obvious that it
-     goes first-to-last. With `compose`, not so much.
-  */
+
+  # note please don’t add a function like `compose = flip pipe`.
+  # This would confuse users, because the order of the functions
+  # in the list is not clear. With pipe, it’s obvious that it
+  # goes first-to-last. With `compose`, not so much.
 
   ## Named versions corresponding to some builtin operators.