chore(wren-ai-service): add readme for config example files (#1295)

wren-ai-service/docs/config_examples/README.md

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+# MUST READ!!!
+
+Since these config files are examples, so **please carefully read the file and comments inside**. Try to understand the purpose of each section and parameter, **don't simply copy and paste the content of these config files into your own config file. It will not work.** For more detailed information to the configurations, please [read this file](../configuration.md).
+
+We also definitely welcome your contribution to add config files for other LLM providers.