implement example

examples/postly/lib/domain/entity/post.dart

@@ -0,0 +1,12 @@
+import 'package:freezed_annotation/freezed_annotation.dart';
+
+part 'post.freezed.dart';
+
+@freezed
+class Post with _$Post {
+  const factory Post({
+    required int id,
+    required String title,
+    required String body,
+  }) = _Post;
+}