[gtk/arnaudb/requires: 3/3] Document the GtkBuilder <requires> tag changes.

[Arnaud B. <arnaudb src gnome org>]

commit 76d8a559bdf73c7dafda0981bd6e011bb7416b7c
Author: Arnaud Bonatti <arnaud bonatti gmail com>
Date:   Sat Nov 7 14:10:41 2020 +0100

    Document the GtkBuilder <requires> tag changes.

 docs/reference/gtk/migrating-3to4.md | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/docs/reference/gtk/migrating-3to4.md b/docs/reference/gtk/migrating-3to4.md
index e3975d8517..14591ecb86 100644
--- a/docs/reference/gtk/migrating-3to4.md
+++ b/docs/reference/gtk/migrating-3to4.md
@@ -445,6 +445,9 @@ gtk4-builder-tool simplify command can perform many of the
 necessary changes automatically, when called with the --3to4
 option. You should always review the resulting changes.
 
+The <requires> tag now supports for the 'lib' attribute the
+'gtk' value only, instead of the 'gtk+' one previously.
+
 ### Adapt to event controller API changes
 
 A few changes to the event controller and #GtkGesture APIs