add link to rustc_smir

Author: RalfJung

README.md

@@ -24,8 +24,11 @@ This is the repository we use to organise our work. Please refer to our [charter
 as our [github pages website][gh-pages] for more information on our goals and
 current scope.
 
+If you are wondering how to use Stable MIR in your project, also see the [rustc_smir crate].
+
 [charter]: ./CHARTER.md
 [gh-pages]: https://rust-lang.github.io/project-stable-mir
+[rustc_smir]: https://github.com/rust-lang/rust/tree/master/compiler/rustc_smir
 
 
 ## How Can I Get Involved?