Ord as an empty bound example

[gokhanettin]

From Testcase: empty bounds

A consequence of how bounds work is that even if a trait doesn't include any functionality, you can still use it as a bound. Eq and Ord are examples of such traits from the std library.

Unlike std::cmp::Eq, std::cmp::Ord doesn't look like an empty bound in the doc. Is it a correct example for empty bounds?

If it is not, we can change with std::marker::Sync and std::marker::Send maybe?