Update OpenAI error handling

Author: atesgoral

README.md

@@ -180,7 +180,7 @@ puts response.dig("choices", 0, "message", "content")
 
 [Quick guide to streaming ChatGPT with Rails 7 and Hotwire](https://gist.github.com/alexrudall/cb5ee1e109353ef358adb4e66631799d)
 
-You can stream from the API in realtime, which can be much faster and used to create a more engaging user experience. Pass a [Proc](https://ruby-doc.org/core-2.6/Proc.html) (or any object with a `#call` method) to the `stream` parameter to receive the stream of text chunks as they are generated. Each time one or more chunks is received, the proc will be called once with each chunk, parsed as a Hash. If OpenAI returns an error, `ruby-openai` will pass that to your proc as a Hash.
+You can stream from the API in realtime, which can be much faster and used to create a more engaging user experience. Pass a [Proc](https://ruby-doc.org/core-2.6/Proc.html) (or any object with a `#call` method) to the `stream` parameter to receive the stream of completion chunks as they are generated. Each time one or more chunks is received, the proc will be called once with each chunk, parsed as a Hash. If OpenAI returns an error, `ruby-openai` will raise an error.
 
 ```ruby
 client.chat(