[libsoup/wip/docs-threading] docs: Add clarification on threading

[Patrick Griffis <pgriffis src gnome org>]

commit 6ba415885e332ac0d34e0f03686105870e937276
Author: Patrick Griffis <pgriffis igalia com>
Date:   Sat Apr 17 14:35:43 2021 -0500

    docs: Add clarification on threading

 docs/reference/migrating-from-libsoup-2.xml | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/docs/reference/migrating-from-libsoup-2.xml b/docs/reference/migrating-from-libsoup-2.xml
index 74f2e375..50c5ba29 100644
--- a/docs/reference/migrating-from-libsoup-2.xml
+++ b/docs/reference/migrating-from-libsoup-2.xml
@@ -182,5 +182,11 @@ linkend="soup-uri-decode-data-uri"><function>soup_uri_decode_data_uri()</functio
                 <link 
linkend="soup_message_set_request_body_from_bytes"><function>soup_message_set_request_body_from_bytes()</function></link>
 to use a GBytes
             buffer.</para>
     </sect2>
+    <sect2 id="threading">
+        <title>Clarification on thread-safety</title>
+        <para>In libsoup 2 there was an attempt at making various APIs of the library thread-safe; However 
this was never well tested, maintained, or documented.</para>
+        <para>In libsoup 3 it now behaves in-line with other GObject libraries. Once you create a <link 
linkend="SoupSession"><type>SoupSession</type></link> all usage of that
+            session must happen on the same thread. You may create seperate sessions per thread but in most 
use-cases you should be using the async APIs which handle non-blocking IO for you.</para>
+    </sect2>
 </chapter>