[gtk] Mention 'main' branch in NEWS

[Matthias Clasen <matthiasc src gnome org>]

commit 0579220546f7daff16a907f4c3256098c344e40c
Author: Matthias Clasen <mclasen redhat com>
Date:   Mon Nov 29 18:09:27 2021 -0500

    Mention 'main' branch in NEWS
    
    The default development branch is now `main`.
    This commit only exists on `master` to point people
    towards that.

 NEWS | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/NEWS b/NEWS
index 7704dbe329..ea9f7b6ede 100644
--- a/NEWS
+++ b/NEWS
@@ -1,3 +1,8 @@
+Overview of Changes
+===================
+
+* Rename git `master` branch to `main`
+
 Overview of Changes in 4.5.0
 ============================