[libsoup/pgriffis/context-documentation] session: Document which context callbacks will be invoked on

[Patrick Griffis <pgriffis src gnome org>]

commit 8fb1dc96554cf5e624229ca3c58555e4ecb24e65
Author: Patrick Griffis <pgriffis igalia com>
Date:   Mon Jan 10 17:49:43 2022 +0000

    session: Document which context callbacks will be invoked on

 libsoup/soup-session.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/libsoup/soup-session.c b/libsoup/soup-session.c
index ce9bbf9d..02b60daf 100644
--- a/libsoup/soup-session.c
+++ b/libsoup/soup-session.c
@@ -3338,6 +3338,9 @@ soup_session_return_error_if_message_already_in_queue (SoupSession         *sess
  * Call soup_session_send_finish() to get a #GInputStream for reading
  * the response body.
  *
+ * The @callback will be invoked on the thread-default context at the time
+ * when this function is called.
+ *
  * See soup_session_send() for more details on the general semantics.
  *
  */