clarify turbo vs instruct a bit more

Author: Keiji Kanazawa

articles/ai-services/openai/concepts/models.md

@@ -38,7 +38,7 @@ The `gpt-4` model supports 8192 max input tokens and the `gpt-4-32k` model suppo
 
 ## GPT-3.5
 
-GPT-3.5 models can understand and generate natural language or code. The most capable and cost effective model in the GPT-3.5 family is GPT-3.5 Turbo, which has been optimized for chat and works well for traditional completions tasks as well.  GPT-3.5 Turbo Instruct has similar capabilities to `text-davinci-003` using the Completions API instead of the Chat Completions API.  We recommend using GPT-3.5 Turbo and GPT-3.5 Turbo Instruct over [legacy GPT-3.5 and GPT-3 models](./legacy-models.md).
+GPT-3.5 models can understand and generate natural language or code. The most capable and cost effective model in the GPT-3.5 family is GPT-3.5 Turbo, which has been optimized for chat and works well for traditional completions tasks as well. GPT-3.5 Turbo is available for use with the Chat Completions API. GPT-3.5 Turbo Instruct has similar capabilities to `text-davinci-003` using the Completions API instead of the Chat Completions API.  We recommend using GPT-3.5 Turbo and GPT-3.5 Turbo Instruct over [legacy GPT-3.5 and GPT-3 models](./legacy-models.md).
 
 - `gpt-35-turbo`
 - `gpt-35-turbo-16k`