Agreed! There are plenty of people that have links to their own websites, including those that aren’t obviously related to iNat but are just part of their lives. If the books are relevant to what you do on iNat, I think it’s totally appropriate to mention that you’ve written them/list them.
I think that there probably is a line somewhere for self-promotional profile content that wouldn’t be ok (explicitly trying to sell something, links to a commercial site that directly profit you, etc.), but I think that there’s plenty of opportunity to post without going that far.