While not a big problem you can simply insert this code snippet in a WordPress PHP file that suits. A good place is in your footer.php file where the message "Proudly powered by WordPress" lies. A text display of the WordPress websites author's name or perhaps a link to the author's profile
<span class='vcard author'>
<span class='fn'>
Site author <a href='https://web address of you profile if you wish">Fred etc</a>
</span>
</span>