[Docs]There are errors in the usage of OpenAI in the README file

[leixiaotian1]

Is your report related to a problem? Please describe.
The use of the OpenAI plugin described in the file at openAI readme is incorrect.

Is your report related to a suggestion/improvement? Please describe.
change oai := openai.NewPlugin(apiKey) to oai := &openai.OpenAI{APIKey: apiKey,}

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