I often build WordPress sites for clients using the Headway framework, and one common task across all sites is adding my credit to the footer. Luckily, this is incredibly simple to do! You can take two different approaches:
Use the Custom Copyright Input Field
Open up the block options for the footer block, and you’ll see a box for a Custom Copyright. This input will accept plain text and HTML, so you can code up your own little copyright for your client with your credit included.
Copyright © 2013 My Client. Site Designed by <a href="http://mysite.com">My Company</a>. All Rights Reserved.
Drop a Text Block Below your Footer
You could also opt to use the normal footer & show your client’s copyright there – then put a Text Block below that footer and use the provided WYSIWYG to enter your link, credit, whatever!