Document how to pass value for userstyles

In README there is only [`userscripts`](https://github.com/AdguardTeam/ReportsWebApp#:~:text=by%20commas.-,userscripts,-An%20url%2Dencoded) parameter which is outdated because now AdGuard apps use `extensions.enabled` and `extensions` parameters for that. But for new userstyles I can't find the correct parameter.