View source to find the proper RSS feed discovery tags, which is what RSS readers actually do… don’t just randomly slap .rss on the end of URLs, no matter what @pfaffman says 
<link rel="alternate" type="application/rss+xml" title="RSS feed of 'Can we add "feed" function on Discourse?'" href="https://meta.discourse.org/t/can-we-add-feed-function-on-discourse/57987.rss" />