add changelog

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/ChangeLog.d/fix-null-dereference-verify-ext.txt b/ChangeLog.d/fix-null-dereference-verify-ext.txt
new file mode 100644
index 0000000..4654178
--- /dev/null
+++ b/ChangeLog.d/fix-null-dereference-verify-ext.txt
@@ -0,0 +1,3 @@
+Bugfix
+   * Fix NULL pointer dereference in mbedtls_pk_verify_ext() when called using
+     an opaque RSA context and specifying MBEDTLS_PK_RSASSA_PSS as key type.