[gtk/wip/issue-21] Mention gtk_button_set_image() and friends in the migration docs

[Emmanuele Bassi <ebassi src gnome org>]

commit 7ee69fc7b21cad5ff322d72b0b6f5720bb0765b2
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Tue Feb 13 12:57:18 2018 +0000

    Mention gtk_button_set_image() and friends in the migration docs
    
    The image-related API for GtkButton has been dropped, but still needs
    to be mentioned in the migration guide.
    
    Closes: #21

 docs/reference/gtk/migrating-3to4.xml | 12 ++++++++++++
 1 file changed, 12 insertions(+)
---
diff --git a/docs/reference/gtk/migrating-3to4.xml b/docs/reference/gtk/migrating-3to4.xml
index 46327e43af..a162b5e5f0 100644
--- a/docs/reference/gtk/migrating-3to4.xml
+++ b/docs/reference/gtk/migrating-3to4.xml
@@ -157,6 +157,18 @@
       </para>
     </section>
 
+    <section>
+      <title>Stop using GtkButton's image-related API</title>
+      <para>
+        The functions and properties related to automatically add a GtkImage
+        to a GtkButton, and using a GtkSetting to control its visibility, are
+        not supported in GTK+ 4. Instead, you can just pack a GtkImage inside
+        a GtkButton, and control its visibility like you would for any other
+        widget. If you only want to add a named icon to a GtkButton, you can
+        use gtk_button_set_icon_name().
+      </para>
+    </section>
+
   </section>
 
   <section>