Update humor docs for special-casing ferris emoji

update for: https://github.com/rust-lang/rust/pull/91476/files

Author: mheiber

Diff for: src/appendix/humorust.md

@@ -11,3 +11,4 @@ enlightening?
 - [`break rust;`](https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=0ab2bd6a9d722e0f05a95e2a5dcf89cc)
 - [The Nomicon Intro](https://doc.rust-lang.org/stable/nomicon/)
 - [`rustc-ty` renaming punfest](https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/rustc-ty.20naming.20bikeshed.20.2F.20punfest.20%28was.3A.20design.20meeting.202.2E.2E.2E/near/189906455)
+- [try using their name "ferris" instead](https://github.com/rust-lang/rust/pull/91476)