Update acknowledgments

README.md

@@ -101,3 +101,4 @@ Special thanks to the following users and organizations for generously supportin
 <a href="https://opencollective.com/tabulapdf/backer/5/website" target="_blank"><img src="https://opencollective.com/tabulapdf/backer/5/avatar"></a>
 
 <a title="The John S. and James L. Knight Foundation" href="http://www.knightfoundation.org/" target="_blank"><img alt="The John S. and James L. Knight Foundation" src="http://www.knightfoundation.org/media/uploads/media_images/knight-logo-300.jpg"></a>
+<a title="The Shuttleworth Foundation" href="https://shuttleworthfoundation.org/" target="_blank"><img width="200" alt="The Shuttleworth Foundation" src="https://raw.githubusercontent.com/tabulapdf/tabula/gh-pages/shuttleworth.jpg"></a>