Minor language update. (#5261)

How about adding 'for example' to create room for other natural cases?

src/effective-dart/design.md

@@ -619,8 +619,8 @@ class _Favorites {
 In idiomatic Dart, classes define *kinds of objects*. A type that is never
 instantiated is a code smell.
 
-However, this isn't a hard rule. With constants and enum-like types, it may be
-natural to group them in a class.
+However, this isn't a hard rule. For example, with constants and enum-like types,
+it may be natural to group them in a class.
 
 {:.good}
 <?code-excerpt "design_bad.dart (class-only-static-exception)"?>