message: Longer README about how to use this instead of `cargo run`
  * Longer README about how to use this instead of `cargo run`
  Resolves
diff: @@ -13,14 +13,20 @@ $ ./test.sh --release
  ## Usage
  -`$cg_clif_dir` is the directory you cloned this repo into in the following instructions.
  +rustc_codegen_cranelift can be used as a near-drop-in replacement for `cargo build` or `cargo run` for existing projects.
  +
  +Assuming `$cg_clif_dir` is the directory you cloned this repo into and you followed the instructions (`prepare.sh` and `test.sh`).
  ### Cargo
  +In the directory with your project (where you can do the usual `cargo build`), run:
  +
  ```bash
  $ CHANNEL="release" $cg_clif_dir/cargo.sh run
  ```
  +This should build and run your project with rustc_codegen_cranelift instead of the usual LLVM backend.
  +
  If you compiled cg_clif in debug mode (aka you didn't pass `--release` to `./test.sh`) you should use `CHANNEL="debug"` instead or omit `CHANNEL="release"` completely.
  ### Rustc
  