Add Changelog entry

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/ChangeLog.d/fix-cipher-output-size-macros.txt b/ChangeLog.d/fix-cipher-output-size-macros.txt
new file mode 100644
index 0000000..4a4b971
--- /dev/null
+++ b/ChangeLog.d/fix-cipher-output-size-macros.txt
@@ -0,0 +1,4 @@
+Bugfix
+   * Prevent divide by zero if either of PSA_CIPHER_ENCRYPT_OUTPUT_SIZE() or
+     PSA_CIPHER_UPDATE_OUTPUT_SIZE() were called using an asymmetric key type.
+