docs: add docs for voice focus and audio normalization features

Author: slee-aws

README.md

@@ -19,6 +19,13 @@ Follow these instructions to run the demo:
 2. Run: `npm run dev`
 3. Enter an `API_URL`, if prompted. The app will attempt to automatically retrieve an `API_URL` from your AWS account. If you do not have an `API_URL`, follow the instructions in the [Serverless README](./infra/README.md) of this repository.
 
+## Additional documentation
+
+Additional documentation for the following features is available in the `docs/` directory:
+
+- [Amazon Voice Focus](./docs/voice-focus.md): AI-powered noise suppression
+- [Audio Normalization](./docs/audio-normalization.md): Automatically normalize the volume levels of remote participants
+
 ## Known issues and limitations
 
 - The application is meant for demonstration purposes and **not** for production use.