[glib] gqueue: Document to use GAsyncQueue for thread-safe queuing

[Philip Withnall <pwithnall src gnome org>]

commit 1f20ddbb5598e19c6230af268081d434f492375d
Author: Philip Withnall <withnall endlessm com>
Date:   Tue May 15 12:50:21 2018 +0100

    gqueue: Document to use GAsyncQueue for thread-safe queuing
    
    Signed-off-by: Philip Withnall <withnall endlessm com>
    Reviewed-by: nobody

 glib/gqueue.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/glib/gqueue.c b/glib/gqueue.c
index 26fe507a3..bf172f6ff 100644
--- a/glib/gqueue.c
+++ b/glib/gqueue.c
@@ -35,6 +35,9 @@
  * using one of the [Type Conversion Macros][glib-Type-Conversion-Macros],
  * or simply pointers to any type of data.
  *
+ * As with all other GLib data structures, #GQueue is not thread-safe.
+ * For a thread-safe queue, use #GAsyncQueue.
+ *
  * To create a new GQueue, use g_queue_new().
  *
  * To initialize a statically-allocated GQueue, use #G_QUEUE_INIT or