nix: add a comment about makeScope

.devops/nix/scope.nix

@@ -4,6 +4,10 @@
   llamaVersion ? "0.0.0",
 }:
 
+# We're using `makeScope` instead of just writing out an attrset
+# because it allows users to apply overlays later using `overrideScope'`.
+# Cf. https://noogle.dev/f/lib/makeScope
+
 lib.makeScope newScope (
   self: {
     inherit llamaVersion;