docs: limitations of latest realtime voice (#43)

Author: bryantanderson

fern/openai-realtime.mdx

@@ -12,5 +12,5 @@ OpenAI’s Realtime API enables developers to use a native speech-to-speech mode
 
 To start using it with your Vapi assistants, select `gpt-4o-realtime-preview-2024-10-01` as your model. 
 - Please note that only OpenAI voices may be selected while using this model. The voice selection will not act as a TTS (text-to-speech) model, but rather as the voice used within the speech-to-speech model.
-- Also note that we don’t currently support Knowledge Bases with the Realtime API.
+- Also note that we don’t currently support Knowledge Bases with the Realtime API. Furthermore, advanced functionality is currently limited with the latest voices Ash, Ballad, Coral, Sage and Verse.
 - Lastly, note that our Realtime integration still retains the rest of Vapi's orchestration layer such as the endpointing and interruption models to enable a reliable conversational flow.