Include the Atom feed format in your description of feeds

[Neurogami]

In addition to RSS (in its many flavors) there is also the Atom feed format

https://validator.w3.org/feed/docs/atom.html

Most of the time a site that offers Atom also offers some form of RSS, but there are cases of atom-only feeds and folks should be aware of them.

[j-f1]

There's also JSON feeds which are less popular but also supported by many feed readers.

[zcdunn]

There's also h-feed which is way less supported but is a part of the IndieWeb collection of technologies and easy to implement on a homegrown blog.