update readme for @nestjs/swagger v4 usage

[mutoe]

What kind of change does this PR introduce(这个 PR 引入了什么样的变化)?

• Bugfix(修正错误)
• Feature(新功能)
• Refactor(重构)
• Build-related changes(与构建相关的更改)
• Other, please describe(其他，请描述): 更新使用文档

Does this PR introduce a breaking change(这次 PR 引入了一个重大变化吗)?

• Yes(是)
• No(否)

If yes, please describe the impact and migration path for existing applications(如果是，请描述现有应用程序的影响和迁移路径):

The PR fulfills these requirements(PR 符合以下要求)

• All tests are passing(所有测试都通过)

Other information(其他信息)

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