[gtk/matthiasc/surface-state-rework: 80/80] Mention window sizes in the migration guide

[Matthias Clasen <matthiasc src gnome org>]

commit 0f7e0f4ac1f5414cb6d1bab6db4f23c9380370b9
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Dec 5 12:41:52 2020 -0500

    Mention window sizes in the migration guide

 docs/reference/gtk/migrating-3to4.md | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
---
diff --git a/docs/reference/gtk/migrating-3to4.md b/docs/reference/gtk/migrating-3to4.md
index 95847872f7..c4024c9c2f 100644
--- a/docs/reference/gtk/migrating-3to4.md
+++ b/docs/reference/gtk/migrating-3to4.md
@@ -510,9 +510,14 @@ gtk_window_set_gravity(), gtk_window_move(), gtk_window_parse_geometry(),
 gtk_window_set_keep_above(), gtk_window_set_keep_below(),
 gtk_window_begin_resize_drag(), gtk_window_begin_move_drag().
 Most likely, you should just stop using them. In some cases, you can
-fall back to using the underlying #GdkToplevel APIS (for example,
+fall back to using the underlying #GdkToplevel APIs (for example,
 gdk_toplevel_begin_resize()).
 
+The APIs for controlling GtkWindow size have changed to be better aligned
+with the way size changes are integrated in the frame cycle. gtk_window_resize()
+and gtk_window_get_size() have been removed. Instead, use
+gtk_window_set_default_size() and gtk_window_get_default_size().
+
 ### Adapt to GtkHeaderBar and GtkActionBar API changes
 
 The gtk_header_bar_set_show_close_button() function has been renamed to