Add missing information about supported subjectAltName types

Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>
diff --git a/include/mbedtls/x509_crt.h b/include/mbedtls/x509_crt.h
index d739237..6c86a66 100644
--- a/include/mbedtls/x509_crt.h
+++ b/include/mbedtls/x509_crt.h
@@ -75,7 +75,7 @@
     mbedtls_x509_buf issuer_id;         /**< Optional X.509 v2/v3 issuer unique identifier. */
     mbedtls_x509_buf subject_id;        /**< Optional X.509 v2/v3 subject unique identifier. */
     mbedtls_x509_buf v3_ext;            /**< Optional X.509 v3 extensions.  */
-    mbedtls_x509_sequence subject_alt_names;    /**< Optional list of raw entries of Subject Alternative Names extension (currently only dNSName, uniformResourceIdentifier and OtherName are listed). */
+    mbedtls_x509_sequence subject_alt_names;    /**< Optional list of raw entries of Subject Alternative Names extension (currently only dNSName, uniformResourceIdentifier, DirectoryName and OtherName are listed). */
 
     mbedtls_x509_sequence certificate_policies; /**< Optional list of certificate policies (Only anyPolicy is printed and enforced, however the rest of the policies are still listed). */