Add Changelog entry

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
new file mode 100644
index 0000000..5843d9e
--- /dev/null
+++ b/ChangeLog.d/cert_write-set-extended-key-usages.txt
@@ -0,0 +1,4 @@
+Features
+   * cert_write: support for setting extended key usage attributes.
+   * cert_write: support for writing certificate files in either PEM
+     or DER format.