Update Changelog

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/ChangeLog.d/cert_write-set-extended-key-usages.txt b/ChangeLog.d/cert_write-set-extended-key-usages.txt
index 5843d9e..02bc801 100644
--- a/ChangeLog.d/cert_write-set-extended-key-usages.txt
+++ b/ChangeLog.d/cert_write-set-extended-key-usages.txt
@@ -1,4 +1,6 @@
 Features
-   * cert_write: support for setting extended key usage attributes.
+   * cert_write: support for setting extended key usage attributes. A
+     corresponding new public API call has been added in the library,
+     mbedtls_x509write_crt_set_ext_key_usage.
    * cert_write: support for writing certificate files in either PEM
      or DER format.