add changelog

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/ChangeLog.d/8709.txt b/ChangeLog.d/8709.txt
new file mode 100644
index 0000000..52b9609
--- /dev/null
+++ b/ChangeLog.d/8709.txt
@@ -0,0 +1,3 @@
+Features
+   * The new function mbedtls_pk_copy_from_psa() provides a way to setup
+     a PK context starting from a PSA key.