Documentation doesn't include examples of how to use `reasoning` parameter

[gadenbuie]

I had to read through the PRs that added reasoning to figure out what kind of argument should be provided

• feat: better support for reasoning/thinking #202
• feat: add reasoning parameter to ChatAzureOpenAI() #260
• feat: add reasoning parameter to ChatBedrockAnthropic() #286
• fix(deepseek): support reasoning_content in tools and streaming #288