update readme with reference to the old version

Author: liv

README.md

@@ -4,6 +4,8 @@
 
 Greetings and welcome to `rustlings`. This project contains small exercises to get you used to reading and writing Rust code. This includes reading and responding to compiler messages!
 
+_...looking for the old, web-based version of Rustlings? Try [here](https://github.com/rustlings/rustlings/tree/rustlings-1)_
+
 Alternatively, for a first-time Rust learner, there's several other resources:
 
 - [The Book](https://doc.rust-lang.org/book/index.html) - The most comprehensive resource for learning Rust, but a bit theoretical sometimes. You will be using this along with Rustlings!