functional/stateful-types.md: add second link

Author: jhwgh1968

functional/stateful-types.md

@@ -244,5 +244,5 @@ There are a number of simpler state machines, however, that have their own patte
 ## See also
 
 * [The Case for the Type State Pattern](https://web.archive.org/web/20210325065112/https://www.novatec-gmbh.de/en/blog/the-case-for-the-typestate-pattern-the-typestate-pattern-itself/)
-* FIXME: I remember seeing a Rust talk which described this in more detail, but I
+* [Rusty Typestate Series (an extensive thesis)](https://web.archive.org/web/20210328164854/https://rustype.github.io/notes/notes/rust-typestate-series/rust-typestate-index)
 can't find it again.