[gimp/gimp-2-10] app: add link to Smart Colorization scientific paper.

[Jehan <jehanp src gnome org>]

commit 4fd8e4841f5ba142341229d875437c5c2e36d77c
Author: Jehan <jehan girinstud io>
Date:   Sat Jan 12 00:26:19 2019 +0100

    app: add link to Smart Colorization scientific paper.
    
    This is sometimes asked, and myself also need to find it from time to
    time. I may as well put the link inside the code comments, where it is
    just easy to find!
    
    (cherry picked from commit 005bc1406bede5abdae965a52b636b8c511f7e6f)

 app/core/gimplineart.c | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/app/core/gimplineart.c b/app/core/gimplineart.c
index 09910357c6..de67cf7d96 100644
--- a/app/core/gimplineart.c
+++ b/app/core/gimplineart.c
@@ -792,6 +792,7 @@ gimp_line_art_input_invalidate_preview (GimpViewable *viewable,
  * The algorithm is the first step from the research paper "A Fast and
  * Efficient Semi-guided Algorithm for Flat Coloring Line-arts", by Sébastian
  * Fourey, David Tschumperlé, David Revoy.
+ * https://hal.archives-ouvertes.fr/hal-01891876
  *
  * Returns: a new #GeglBuffer of format "Y u8" representing the
  *          binarized @line_art. If @lineart_distmap is not #NULL, a