README was incorrect with instructions on how to use the gem:
 - the first two examples referenced an incorrect module name (WebDriver
   instead of webdriver)
 - the watir webdriver example did not include a reference to the
   Webdriver module causing a "NameError: uninitialized constant
UserAgent" error to be thrown when following the documentation
Merge pull request #14 from christemple/watir-webdriver-readme-fix

README was incorrect with instructions on how to use the gem: