Fix package_todo update comment

The update-todo subcommand with arguments has been deprecated and is no
longer supported.

lib/packwerk/package_todo.rb

@@ -101,7 +101,7 @@ def dump
           #
           # You can regenerate this file using the following command:
           #
-          # bin/packwerk update-todo #{@package.name}
+          # bin/packwerk update-todo
         MESSAGE
         File.open(@filepath, "w") do |f|
           f.write(message)

test/unit/packwerk/package_todo_test.rb

@@ -224,6 +224,32 @@ class PackageTodoTest < Minitest::Test
       end
     end
 
+    test "#dump dumps package TODO comment" do
+      Tempfile.create("test_file.yml") do |file|
+        package_todo = PackageTodo.new(destination_package, file.path)
+        first_package = Package.new(name: "some_package", config: {})
+        first_package_reference = build_reference(
+          destination_package: first_package,
+          constant_name: "::Checkout::Wallet",
+          path: "some/violated/path.rb"
+        )
+
+        package_todo.add_entries(first_package_reference,
+          ReferenceChecking::Checkers::DependencyChecker::VIOLATION_TYPE)
+        package_todo.dump
+
+        assert_equal(<<~YAML, file.readlines.first(7).join)
+          # This file contains a list of dependencies that are not part of the long term plan for buyers.
+          # We should generally work to reduce this list, but not at the expense of actually getting work done.
+          #
+          # You can regenerate this file using the following command:
+          #
+          # bin/packwerk update-todo
+          ---
+        YAML
+      end
+    end
+
     test "#dump deletes the package TODO if there are no entries" do
       file = Tempfile.new("empty_package_todo.yml")
       package_todo = PackageTodo.new(destination_package, T.must(file.path))