Here is the RSS feed of Hacker News: https://news.ycombinator.com/rss
Edit:
Every single of those webpages have an RSS feed.
Ars Technica: http://feeds.arstechnica.com/arstechnica/index/
The Guardian: https://www.theguardian.com/uk/rss
LWN: https://lwn.net/headlines/newrss
BBC: http://feeds.bbci.co.uk/news/video_and_audio/news_front_page...