add example Behat

[tyler36]

Fixes #21

This PR adds an example snippet for using this addon with Drupal and Behat.

I kept the base_url as http to match the environmental variables you have set in config.selenium-standalone-chrome.yaml

If base_url is set to https://web, an additional switch is required: - "--ignore-certificate-errors".

Tested

• Works asBehat\MinkExtension extension
• Works when changing to Drupal\MinkExtension extension
• Comment out - "--headless" to watch in noVNC

Note: if I commented out the capabilities section, Behat freezes. It didn't seem to matter what switches I used, as long as it was there.

[bserem]

Approved!

I tested this, works flawlessly.