Fix ChangeLog entry for FFDH in PSA

It was jumping directly to "driver support" and omitting the first step
of "PSA support".

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/ChangeLog.d/driver-ffdh.txt b/ChangeLog.d/driver-ffdh.txt
index 1185133..a9fa641 100644
--- a/ChangeLog.d/driver-ffdh.txt
+++ b/ChangeLog.d/driver-ffdh.txt
@@ -1,3 +1,5 @@
 Features
-   * Add a driver dispatch layer for FFDH keys, enabling alternative
+   * Add support for the FFDH algorithm and DH key types in PSA, with
+     parameters from RFC 7919. This includes a built-in implementation based
+     on MBEDTLS_BIGNUM_C, and a driver dispatch layer enabling alternative
      implementations of FFDH through the driver entry points.