message: Add submodule checkout command
diff: @@ -32,8 +32,11 @@ The library should build and pass all tests.
  $ git clone https://github.com/xpring-eng/xpring-js.git
  $ cd xpring-js
  +# Pull Submdoules
  +$ git submodule update --init --recursive
  +
  # Install dependencies
  -npm i
  +$ npm i
  # Install gRPC Web
  ## OSX
  