Added model names (run-llama#578)

docs/how_to/custom_llms.md

@@ -28,7 +28,7 @@ Below we show a few examples of LLM customization. This includes
 ## Example: Changing the underlying LLM
 
 An example snippet of customizing the LLM being used is shown below. 
-In this example, we use `text-davinci-002` instead of `text-davinci-003`. Note that 
+In this example, we use `text-davinci-002` instead of `text-davinci-003`. Available models include `text-davinci-003`,`text-curie-001`,`text-babbage-001`,`text-ada-001`, `code-davinci-002`,`code-cushman-001`. Note that 
 you may plug in any LLM shown on Langchain's 
 [LLM](https://langchain.readthedocs.io/en/latest/modules/llms.html) page.