SKILL.md says Firefox is a prerequisite, but README.md doesn't.

In https://github.com/microsoft/Webwright/blob/main/skills/webwright/SKILL.md

### Prerequisites (one-time)

From the Webwright repo root:

```
playwright install firefox
```

---

In https://github.com/microsoft/Webwright/blob/main/README.md

### Prerequisites

- Python 3.10+
- Chromium installed through Playwright
- An API key for your chosen backend (OpenAI, Anthropic, or OpenRouter)