message: Added clone '--depth=1' option to readme
diff: First, clone the repo via git:
  ```bash
  -git clone https://github.com/chentsulin/electron-react-boilerplate.git your-project-name
  +git clone --depth=1 https://github.com/chentsulin/electron-react-boilerplate.git your-project-name
  ```
  And then install dependencies.
  