Leanpub authors appreciate being told about typos and things like that - thank you very much for your interest in doing this.

On most Leanpub books, if you go to the book's landing page on Leanpub and scroll down, you will find a link that says "Email the Author(s)". If you click that link, you will be taken to a form that lets you email the author(s) with information like typos and comments you might have.