message: Clarify scope of language formalisation
diff: # Language formalisation in Lean
  -To work with thes formalisations, you will need to [install Lean 3.3][install_lean].
  +This is incomplete, and mainly indended as an explorative tool to guide the Rust
  +implementation. It would be very nice to provide more guarentees in the future
  +that opur Rust implementation matches this formalisation, but that is out of
  +scope for now!
  +
  +To work with the formalisations, you will need to [install Lean 3.3][install_lean].
  Then run the following commands in the shell:
  ```sh
  