update gif example readme

gif_example/README.md

@@ -1,5 +1,11 @@
 # gif example
 
-Example for writing a Processing sketch that exports an animated gif
+Example for writing a Processing sketch that exports an animated gif. This
+originally [appeared in my
+tumblr](//jordanorelli.com/post/43535803050/one) back in 2013 and
+depends on the
+[extrapixel/gif-animation](//github.com/extrapixel/gif-animation/tree/3.0)
+library, a copy of which is included in the libraries folder of my sketches
+repo.
 
 ![output](export.gif)