Explain downgrade of per-user installs (#328)

This improves the package downgrade documentation by explaining how to downgrade packages that were installed per-user.

Co-authored-by: Patrick <tingping@tingping.se>

docs/tips-and-tricks.rst

@@ -41,6 +41,10 @@ Then you deploy the commit::
    --commit=ec07ad6c54e803d1428e5580426a41315e50a14376af033458e7a65bfb2b64f0 \
    org.gnome.Recipes
 
+.. note::
+
+   The example here uses ``sudo`` for system installations because, unlike normal updates, downgrades are considered a privileged action. If the application is installed per-user you would run it as that user.
+
 If you have Flatpak 1.5.0 or later, you can also prevent the app from being
 included in updates (either manual or automatic)::