[gtk/matthiasc/for-master] dnd: Add some warnings to the docs

[Matthias Clasen <matthiasc src gnome org>]

commit 74e2bb4cf1cb78fc321619182ea1806e5b87fedc
Author: Matthias Clasen <mclasen redhat com>
Date:   Tue Mar 16 14:24:04 2021 -0400

    dnd: Add some warnings to the docs
    
    Add some warnings about pitfalls of the async dnd api.

 gdk/gdkdrop.c | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/gdk/gdkdrop.c b/gdk/gdkdrop.c
index 4d7ab014f3..cb1cdb1bf6 100644
--- a/gdk/gdkdrop.c
+++ b/gdk/gdkdrop.c
@@ -699,6 +699,11 @@ gdk_drop_read_async (GdkDrop             *self,
  *
  * Finishes an async drop read operation.
  *
+ * Note that you must not use blocking read calls on the returned stream
+ * in the GTK thread, since some platforms might require communication with
+ * GTK to complete the data transfer. You can use async APIs such as
+ * g_input_stream_read_bytes_async().
+ *
  * See [method Gdk Drop.read_async].
  *
  * Returns: (nullable) (transfer full): the `GInputStream`, or %NULL