[libadwaita/wip/exalm/caption] demo: Add a caption to the screenshot

[Alexander Mikhaylenko <alexm src gnome org>]

commit 9dc86c94c322a884a6a8269b40a4adfba56b65af
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Tue Dec 21 13:37:29 2021 +0500

    demo: Add a caption to the screenshot

 demo/data/org.gnome.Adwaita1.Demo.metainfo.xml.in.in | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/demo/data/org.gnome.Adwaita1.Demo.metainfo.xml.in.in 
b/demo/data/org.gnome.Adwaita1.Demo.metainfo.xml.in.in
index c8fe223b..49fd3996 100644
--- a/demo/data/org.gnome.Adwaita1.Demo.metainfo.xml.in.in
+++ b/demo/data/org.gnome.Adwaita1.Demo.metainfo.xml.in.in
@@ -18,6 +18,7 @@
   <screenshots>
     <screenshot type="default">
       
<image>https://gitlab.gnome.org/GNOME/libadwaita/-/raw/main/demo/data/screenshots/screenshot.png</image>
+      <caption>The main window</caption>
     </screenshot>
   </screenshots>