Chromeless: Add Integration Test Sample with Chromeless

[mafshin]

Chromeless is great for real-world integration test. A sample test setup is required in documentation to help the starters.

[adieuadieu]

Hi @mafshin — While we don't yet have any good documentation around this, I wrote a bit about it in https://github.com/graphcool/chromeless/issues/24#issuecomment-319908639

[mafshin]

I added a sample test using Mocha here