[gimp] devel-docs: howto test high density.

[Jehan <jehanp src gnome org>]

commit 67ae36f28e5339762572f6c4264960173e1713de
Author: Jehan <jehan girinstud io>
Date:   Sat May 26 00:32:24 2018 +0200

    devel-docs: howto test high density.

 devel-docs/icons.txt | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)
---
diff --git a/devel-docs/icons.txt b/devel-docs/icons.txt
index f96b694a82..9d16d6b184 100644
--- a/devel-docs/icons.txt
+++ b/devel-docs/icons.txt
@@ -111,4 +111,12 @@ so, set the environment variable `GIMP_ICONS_LIKE_A_BOSS`.
 
 For instance, start GIMP like this:
 
-    GIMP_ICONS_LIKE_A_BOSS=1 gimp-2.10
+    GIMP_ICONS_LIKE_A_BOSS=1 gimp-2.99
+
+To test high (or low) density icons, without having to change the
+scaling factor of your whole desktop, just change the `GDK_SCALE`
+environment variable.
+For instance, run GIMP like this to simulate a scaling factor of 2
+(every icons and text would typically double):
+
+    GDK_SCALE=2 gimp-2.99