[libadwaita/wip/exalm/style-docs: 6/8] doc: Add a missing section to migration guide

[Alexander Mikhaylenko <alexm src gnome org>]

commit 322eb0006977e0bb4619d5e7324048e748e3f9e0
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Wed Dec 15 18:03:21 2021 +0500

    doc: Add a missing section to migration guide
    
    Looks like we only had it in the development version migration guide, but
    not the libhandy -> libadwaita one.

 doc/migrating-libhandy-1-4-to-libadwaita.md | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/doc/migrating-libhandy-1-4-to-libadwaita.md b/doc/migrating-libhandy-1-4-to-libadwaita.md
index ad2c2032..23bd0f40 100644
--- a/doc/migrating-libhandy-1-4-to-libadwaita.md
+++ b/doc/migrating-libhandy-1-4-to-libadwaita.md
@@ -472,6 +472,10 @@ the name of the design pattern. If you were using the
 
 The `.content` style class currently remains for compatibility purposes.
 
+Neither the `.content` style class nor the `.boxed-list` style class work
+for [class@Gtk.ListView], as the widget cannot currently be used for the
+boxed list pattern.
+
 #### Adjusting Icons
 
 If you're bundling icons from the icon library with your application, make sure