[gnome-photos] source-notification: Add a requested translator comment

[Debarshi Ray <debarshir src gnome org>]

commit 7e1ce868cb6d95a66c266035c2e560923226fdd7
Author: Debarshi Ray <debarshir gnome org>
Date:   Mon Feb 20 23:32:07 2017 +0100

    source-notification: Add a requested translator comment

 src/photos-source-notification.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/src/photos-source-notification.c b/src/photos-source-notification.c
index c6c0c14..0aaafbd 100644
--- a/src/photos-source-notification.c
+++ b/src/photos-source-notification.c
@@ -132,6 +132,9 @@ photos_source_notification_constructed (GObject *object)
   gtk_orientable_set_orientation (GTK_ORIENTABLE (self), GTK_ORIENTATION_HORIZONTAL);
 
   name = photos_source_get_name (self->source);
+  /* Translators: %s refers to an online account provider, e.g.,
+   * "Facebook" or "Flickr".
+   */
   msg = g_strdup_printf (_("Your %s credentials have expired"), name);
 
   label = gtk_label_new (msg);