Add note to manual clarifying push/exec and folder-hook order.

Add note to manual clarifying push/exec and folder-hook order.

Folder-hooks are executed in the order declared.  However, push/exec
commands will simply prepend to the keyboard buffer.  If there are
multiple push/exec commands, each will prepend to the earlier one.  The
result is that they will end up being "run" in reverse order once keyboard
buffer processing starts.