[gnome-boxes] preferences: Add note to shared folders UI that it needs spice-webdav

[Felipe Borges <felipeborges src gnome org>]

commit f14920265186c319d711ed88f184eb6d7c708b68
Author: Felipe Borges <felipeborges gnome org>
Date:   Fri Feb 11 11:40:43 2022 +0100

    preferences: Add note to shared folders UI that it needs spice-webdav
    
    Otherwise folder sharing won't work.
    
    Fixes #619

 src/preferences/shared-folders-widget.vala | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)
---
diff --git a/src/preferences/shared-folders-widget.vala b/src/preferences/shared-folders-widget.vala
index 729a5502..106e5b69 100644
--- a/src/preferences/shared-folders-widget.vala
+++ b/src/preferences/shared-folders-widget.vala
@@ -71,10 +71,12 @@ private bool on_popover_saved (string path, string? name) {
     }
 
     private void on_list_updated () {
-        if (list_model.get_n_items () == 0)
-            description = _("Use the button below to add your first shared folder.");
-        else
+        if (list_model.get_n_items () == 0) {
+            // Translators: "spice-webdav" is a name and shouldn't be translated. %s is an URL.
+            description = _("Use the button below to add your first shared folder. For file sharing to work, 
the guest box needs to have <a href='%s'>spice-webdav</a> installed.").printf 
("https://www.spice-space.org/download.html";);
+        } else {
             description = null;
+        }
     }
 }