Make changelog more specific

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/ChangeLog.d/fix-pkcs12-null-password.txt b/ChangeLog.d/fix-pkcs12-null-password.txt
index 699575f..fae8195 100644
--- a/ChangeLog.d/fix-pkcs12-null-password.txt
+++ b/ChangeLog.d/fix-pkcs12-null-password.txt
@@ -1,2 +1,5 @@
 Bugfix
-   * Fix issues in pkcs12 when a NULL and/or zero length password was supplied.
+   * Fix a potential invalid pointer dereference and infinite loop bugs in
+     pkcs12 functions when the password is empty. Fix the documentation to
+     better describe the inputs to these functions and their possible values.
+     Fixes #5136.