Clarify ASN.1 entry named data free functions

Mention the name of the new functions in the "Features" entry. Clarify what
they're for (there's no structure called mbedtls_x509_named_data, it's
mbedtls_asn1_named_data, but that name isn't so important here since we've
mentioned the names of the functions).

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/ChangeLog.d/mbedtls_asn1_type_free.txt b/ChangeLog.d/mbedtls_asn1_type_free.txt
index a6792af..3459bbe 100644
--- a/ChangeLog.d/mbedtls_asn1_type_free.txt
+++ b/ChangeLog.d/mbedtls_asn1_type_free.txt
@@ -1,5 +1,7 @@
 Features
-   * Shared code to free x509 structs like mbedtls_x509_named_data.
+   * The new functions mbedtls_asn1_free_named_data_list() and
+     mbedtls_asn1_free_named_data_list_shallow() simplify the management
+     of memory in named data lists in X.509 structures.
 New deprecations
    * Deprecate mbedtls_asn1_free_named_data().
      Use mbedtls_asn1_free_named_data_list()