[Docs Bug 🐞 report]: README uses wrong environment variable for skipping Chromium download

### Describe the bug you found in AsyncAPI Docs.

The README currently instructs users to set the environment variable `PUPPETEER_SKIP_CHROMIUM_DOWNLOAD` to skip downloading Chromium during installation. However, this environment variable is **deprecated/incorrect** in modern versions of Puppeteer (the project uses `puppeteer@^24.4.0`).

The correct environment variable is `PUPPETEER_SKIP_DOWNLOAD`. Setting `PUPPETEER_SKIP_CHROMIUM_DOWNLOAD=true` has no effect — Chromium is still downloaded. Only `PUPPETEER_SKIP_DOWNLOAD=true` properly prevents the download.

### Attach any resources that can help us understand the issue.

- **Puppeteer official docs on environment variables:** https://pptr.dev/api/puppeteer.configuration#skipdownload
- **Current README location of the issue:** The section in `README.md` that references `PUPPETEER_SKIP_CHROMIUM_DOWNLOAD` should be updated to `PUPPETEER_SKIP_DOWNLOAD`.
- **`package.json` confirms Puppeteer v24+:** https://github.com/asyncapi/html-template/blob/07c8706b2a498c9325bb33248a463fa00ec22469/package.json#L45

### Code of Conduct

- [X] I agree to follow this project's Code of Conduct

### Are you willing to work on this issue?

Yes I am willing to submit a PR!

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Find the Puppeteer environment-variable reference in README.md and compare it with the Puppeteer version shown in package.json. Update the documented variable to PUPPETEER_SKIP_DOWNLOAD, then verify that no README reference still uses PUPPETEER_SKIP_CHROMIUM_DOWNLOAD.

Written by the indexing model from the issue text.