message: Some changes to README.md
diff: ```bash
  $ git clone https://github.com/bjorn3/rustc_codegen_cranelift.git
  $ cd rustc_codegen_cranelift
  -$ ./prepare.sh # downloads and patches sysroot src and installs hyperfine for benchmarking
  +$ ./prepare.sh # download and patch sysroot src and install hyperfine for benchmarking
  $ ./test.sh
  ```
  @@ -18,7 +18,7 @@ $ ./test.sh
  ### Rustc
  ```bash
  -$ rustc -Cpanic=abort -Zcodegen-backend=$cg_clif_dir/target/debug/librustc_codegen_cranelift.so my_crate.rs
  +$ rustc -Cpanic=abort -Zcodegen-backend=$cg_clif_dir/target/debug/librustc_codegen_cranelift.so --sysroot $cg_clif_dir/build_sysroot/sysroot my_crate.rs
  ```
  ### Cargo
  