message: chore: add subsection on nix usage
diff: @@ -12,6 +12,10 @@ If no blue underline is displayed, make sure that Lean 4 is installed correctly
  If the blue underline is displayed but the type is not displayed when hovering over `1`, make sure that you are using a nightly build of Lean 4, not the stable version.
  +### Using the nix setup instead
  +1. Install Lean 4 using [the nix setup](https://leanprover.github.io/lean4/doc/setup.html#nix-setup).
  +2. Create a Lean 4 nix project and run the pinned version of VSCode as described [here](https://leanprover.github.io/lean4/doc/setup.html#basic-commands).
  +
  ## Functionality
  As of now, the extension supports the following features:
  - Diagnostics
  