Add ChangeLog entry

Signed-off-by: Hanno Becker <hanno.becker@arm.com>
diff --git a/ChangeLog.d/session_export_private.txt b/ChangeLog.d/session_export_private.txt
new file mode 100644
index 0000000..5475824
--- /dev/null
+++ b/ChangeLog.d/session_export_private.txt
@@ -0,0 +1,5 @@
+Changes
+    * Explicitly mark the fields mbedtls_ssl_session.exported and
+      mbedtls_ssl_config.respect_cli_pref as private. This was an
+      oversight during the run-up to the release of Mbed TLS 3.0.
+      The fields were never intended to be public.