Use script to handle dependencies and simple test script

Add a shell script to download dependencies and get the test Ruby script. Updates page 2 of tutorial to reflect the change. 

Page is available on my [stew](https://isaac.dev.saucelabs.net/appium/tutorial/2) though the url for the script is in the branch, so the command has to be (at the moment)

```bash
curl -L https://raw.github.com/saucelabs/appium-tutorial/isaac-download/bin/install_tutorial_ruby.sh | bash -s
```

@jlipps