changelog: document MD's conversion functions

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/ChangeLog.d/8664.txt b/ChangeLog.d/8664.txt
new file mode 100644
index 0000000..03e297c
--- /dev/null
+++ b/ChangeLog.d/8664.txt
@@ -0,0 +1,4 @@
+Features
+   * mbedtls_md_psa_alg_from_type() and mbedtls_md_type_from_psa_alg() helper
+     functions were added to convert from mbedtls_md_type_t to psa_algorithm_t
+     and viceversa.