[release-notes/gnome-3-22] add a screenshot for gtk+

[Allan Day <allanday src gnome org>]

commit fe786e23d7b0777a3d8f2d50adca2ea5987e9f28
Author: Allan Day <allanpday gmail com>
Date:   Tue Sep 13 15:08:09 2016 +0100

    add a screenshot for gtk+

 help/C/developers.page             |    2 +-
 help/C/figures/css-blend-modes.png |  Bin 0 -> 272772 bytes
 help/Makefile.am                   |    3 ++-
 3 files changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/help/C/developers.page b/help/C/developers.page
index 4ef2714..d85c41f 100644
--- a/help/C/developers.page
+++ b/help/C/developers.page
@@ -107,7 +107,7 @@
 
   <section id="gtk+">
   <title>GTK+ Improvements</title>
-  <media type="image" src="figures/placeholder.png"/>
+  <media type="image" src="figures/css-blend-modes.png"/>
   <p>In addition to Flatpak portals integration, other improvements in GTK+
   3.22 include:</p>
   <list>
diff --git a/help/C/figures/css-blend-modes.png b/help/C/figures/css-blend-modes.png
new file mode 100644
index 0000000..2349041
Binary files /dev/null and b/help/C/figures/css-blend-modes.png differ
diff --git a/help/Makefile.am b/help/Makefile.am
index 134398d..8b4c080 100644
--- a/help/Makefile.am
+++ b/help/Makefile.am
@@ -15,6 +15,7 @@ HELP_MEDIA = \
  figures/builder.png \
  figures/nautilus-batchrenaming.png \
  figures/keyboard-settings.png \
- figures/photo-sharing.png
+ figures/photo-sharing.png \
+ figures/css-blend-modes.png
 
 HELP_LINGUAS = de el fr gl ko pl