Add example of `.env` file

[pacexy]

This will make it easier for users to set up environment variables.

[lingchuL]

目前代码里是按是否有相应配置来决定要使用OpenAI还是Azure的，并且在检测到有OpenAI的配置会直接使用OpenAI的API尝试，所以如果只是添加用例可能把几行都默认为注释状态比较好~ In the createLanguageModel process, which endpoint to use is determined by whether there is a corresponding configuration to them. It will try to get OpenAI env variable first, once it get the OPENAI_API_KEY, it will use OpenAI as endpoint. Therefore, it may be better to comment all those lines as the default state~

[pacexy]

目前代码里是按是否有相应配置来决定要使用OpenAI还是Azure的，并且在检测到有OpenAI的配置会直接使用OpenAI的API尝试，所以如果只是添加用例可能把几行都默认为注释状态比较好~ In the createLanguageModel process, which endpoint to use is determined by whether there is a corresponding configuration to them. It will try to get OpenAI env variable first, once it get the OPENAI_API_KEY, it will use OpenAI as endpoint. Therefore, it may be better to comment all those lines as the default state~

Maybe we can just keep it empty? (e.g. OPENAI_API_KEY=), and then it will not affect the createLanguageModel.

[lingchuL]

Yeah, it works too.

[Stevenic]

You don't normally include the "" quotes in .env.example files. empty is better

[pacexy]

You don't normally include the "" quotes in .env.example files. empty is better

Updated.