Very nice and readable. May I add some suggestions?
1. The design patterns are presented as they are in the Gang of Four book. It would be good to show (e.g. in a separate readme or a comment in the same source file) what features Kotlin brings that make simplify (and sometimes obviate) some design patterns. For example, the Command Pattern is often replaced by Kotlin's high-order functions and lambda expressions.
2. Alongside the data structures, it would be good to mention in the readme the names of Kotlin Standard Library facilities that implement them (e.g. Queue, LinkedList), so that a learner knows that there already exists a standard implementation and doesn't have to code it themselves.
3. It would be nice to include Timsort, as it's the one that's used by the standard library's Array.sort()