Added instructions for using geckdriver
Added instructions for using geckdriver

In Selenium Standalone Server 3.0.1, Marionette is set to true by default.  Marionette requires a driver for each browser.  Geckodriver is Mozilla's driver for firefox.  I added instructions to download and unpack geckodriver in the project directory, and to specify the driver path when launching Selenium Standalone Server.  If the user does not do this, they will get the error:

Driver info: driver.version: unknown
...
WARN - Exception: The path to the driver executable must be set by the webdriver.gecko.driver system property; for more information, see https://github.com/mozilla/geckodriver. The latest version can be downloaded from https://github.com/mozilla/geckodriver/releases

Please see my test scripts which demonstrate what happens when your run the code in the getting started guide with geckdriver, and without geckodriver at https://github.com/jcreager/webdriverio-getting-started.
monolithed/webdriverio,monolithed/webdriverio