docs: add plugin install and config instructions

[zmstone]

No description provided.

[Meggielqk]

Suggested change

	如果希望插件在 EMQX 启动时即可使用——例如构建自定义 Docker 镜像时——可以提前解压插件包并配置 EMQX。
	如果希望插件在 EMQX 启动时即可使用，例如构建自定义 Docker 镜像时，可以提前解压插件包并配置 EMQX。

[Meggielqk]

Suggested change

	If you want a plugin to be available immediately when EMQX starts — for example, when building a custom Docker image — you can pre-install the plugin by extracting the package and configuring EMQX in advance.
	If you want a plugin to be available immediately when EMQX starts, for example, when building a custom Docker image, you can pre-install the plugin by extracting the package and configuring EMQX in advance.