<link rel="alternate" type="application/rss+xml">
The feed readers' discovery door, open since before social networks.
It declares that the document also exists as a feed. Browsers once showed an orange icon in the address bar when they found this line; the icon is gone, but feed readers and extensions still look for exactly this when someone pastes the site's URL.
It costs one line and asks for no maintenance. The type states the dialect — application/rss+xml or application/atom+xml — and the title tells feeds apart when there is more than one: all articles, comments only, a single section.
<link rel="alternate" type="application/rss+xml"
title="Artigos" href="/feed.xml">