docs: add OpenAI Realtime API (#28)

* add realtime api docs

* nits

Author: bryantanderson

fern/docs.yml

@@ -242,6 +242,8 @@ navigation:
             path: tools-calling.mdx
           - page: Prompting Guide
             path: prompting-guide.mdx
+          - page: OpenAI Realtime 
+            path: openai-realtime.mdx
       - section: Glossary
         contents:
           - page: Definitions

fern/openai-realtime.mdx

@@ -0,0 +1,16 @@
+---
+title: OpenAI Realtime
+subtitle: You can use OpenAI's newest speech-to-speech model with your Vapi assistants.
+slug: openai-realtime
+---
+
+<Note>
+  The Realtime API is currently in beta, and not recommended for production use by OpenAI. We're excited to have you try this new feature and welcome your [feedback](https://discord.com/invite/pUFNcf2WmH) as we continue to refine and improve the experience.
+</Note>
+
+OpenAI’s Realtime API enables developers to use a native speech-to-speech model. Unlike other Vapi configurations which orchestrate a transcriber, model and voice API to simulate speech-to-speech, OpenAI’s Realtime API natively processes audio in and audio out.
+
+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.
+- 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.