message: readme: update git submodule instructions
diff: @@ -38,8 +38,8 @@ rustup toolchain install nightly
  ### Initialization
  ```sh
  -# Initialize the project's submodules
  -git submodule update --init
  +# Initialize the project's submodules and tell cargo to rebuild it
  +git submodule update --init && touch tls/s2n-tls-sys/build.rs
  ```
  ### Running a fuzz target
  