fix styling

overlay.nix

@@ -12,6 +12,9 @@ rec {
         name   = "yosys";
       })
 
+      # NOTE: the version of abc used here is synchronized with
+      # the one in the yosys Makefile of the version above;
+      # keep them the same for quality purposes.
       (super.fetchFromGitHub {
         owner  = "berkeley-abc";
         repo   = "abc";