doc: add zulip link

Author: manyinsects

README.md

@@ -154,6 +154,10 @@ Now you should be done!
 
 See [CONTRIBUTING.md](./CONTRIBUTING.md).
 
+Development-focused discussion about Rustlings happens in the [**rustlings** stream](https://rust-lang.zulipchat.com/#narrow/stream/334454-rustlings)
+on the [Rust Project Zulip](https://rust-lang.zulipchat.com). Feel free to start a new thread there
+if you have ideas or suggestions!
+
 ## Contributors ✨
 
 Thanks goes to the wonderful people listed in [AUTHORS.md](./AUTHORS.md) 🎉