Add image credit (#55)

Author: morevnaproject

source/releases/stable/1.4.3.md

@@ -27,7 +27,7 @@ Synfig Studio 1.4.3 introduces major performance optimizations for Windows users
 ### Improvements
 
 ```{image} 1.4.3_dat/wrong-bone-link.png
-:alt: Wrong bone link warning
+:alt: Wrong bone link warning. Artwork by David Revoy (CC-BY).
 :width: 400px
 ```