Adding attribution for the hero image

Author: escowles

_data/conf.yml

@@ -17,7 +17,7 @@ catchline:
 ###########################
 # Place hero image in /assets/img/theme-images/. Includes optional webp format.
 hero-image-filename: 'hero-image.jpg'
-hero-image-source: ''
+hero-image-source: 'Courtesy of Heidi Wiren Kebe'
 hero-image-filename-webp: 'hero-image.webp'
 hero-image-alt: "Photo of the Mellon Institute Library at Carnegie Mellon University, with yellow leaves."