Add ChangeLog entry for CMake config defines

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/ChangeLog.d/cmake-pass-through-config-defines.txt b/ChangeLog.d/cmake-pass-through-config-defines.txt
new file mode 100644
index 0000000..6122f37
--- /dev/null
+++ b/ChangeLog.d/cmake-pass-through-config-defines.txt
@@ -0,0 +1,3 @@
+Features
+   * Allow MBEDTLS_CONFIG_FILE and MBEDTLS_USER_CONFIG_FILE to be set by
+     setting the CMake variable of the same name at configuration time.