Facial Action Units - feature extraction method

### Have you read the Contributing Guidelines?

- [x] I have read the [Contributing Guidelines](https://github.com/facebookresearch/seamless_interaction/blob/main/CONTRIBUTING.md).

### Documentation Type

Missing documentation

### Documentation Issue Description

Hi,

Thank you for sharing this work and the dataset. We are wondering what method you used to extract FAUs?
For example iMotions/ open face/media pipe?

Many thanks

### Affected Documentation

README.md - Movement/Imitator Feature Types

### Suggested Improvement

Clarification as to whether FAUs were extracted with a specific software or custom method

### Current Documentation Problem

_No response_

### Self-service

- [ ] I'd be willing to address this documentation request myself.