Add ChangeLog entry for string_to_names() fix

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/ChangeLog.d/fix-string-to-names-retcode.txt b/ChangeLog.d/fix-string-to-names-retcode.txt
new file mode 100644
index 0000000..ac4b3d1
--- /dev/null
+++ b/ChangeLog.d/fix-string-to-names-retcode.txt
@@ -0,0 +1,3 @@
+Bugfix
+   * Fix a bug in which mbedtls_x509_string_to_names() would return success
+     when given a invalid name string if it did not contain '=' or ','.