"how readers can interpret" is a noun clause (though it seems to be lacking something after "interpret"). "how" is an adverb, but not a relative one. In fact, I can't think of any examples of "how" as a relative adverb.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
I can't think of any examples of "how" as a relative adverb.